HTTP/1.1, part 1: URIs, Connections, and Message ParsingDay Software23 Corporate Plaza DR, Suite 280Newport BeachCA92660USA+1-949-706-5300+1-949-706-5305fielding@gbiv.comhttp://roy.gbiv.com/Alcatel-Lucent Bell Labs21 Oak Knoll RoadCarlisleMA01741USAjg@freedesktop.orghttp://gettys.wordpress.com/Hewlett-Packard CompanyHP Labs, Large Scale Systems Group1501 Page Mill Road, MS 1177Palo AltoCA94304USAJeffMogul@acm.orgMicrosoft Corporation1 Microsoft WayRedmondWA98052USAhenrikn@microsoft.comAdobe Systems, Incorporated345 Park AveSan JoseCA95110USALMM@acm.orghttp://larry.masinter.net/Microsoft Corporation1 Microsoft WayRedmondWA98052paulle@microsoft.comWorld Wide Web ConsortiumMIT Computer Science and Artificial Intelligence LaboratoryThe Stata Center, Building 3232 Vassar StreetCambridgeMA02139USAtimbl@w3.orghttp://www.w3.org/People/Berners-Lee/World Wide Web ConsortiumW3C / ERCIM2004, rte des LuciolesSophia-AntipolisAM06902Franceylafon@w3.orghttp://www.raubacapeu.net/people/yves/greenbytes GmbHHafenweg 16MuensterNW48155Germany+49 251 2807760+49 251 2807761julian.reschke@greenbytes.dehttp://greenbytes.de/tech/webdav/HTTPbis Working Group
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypertext information
systems. HTTP has been in use by the World Wide Web global information
initiative since 1990. This document is Part 1 of the seven-part specification
that defines the protocol referred to as "HTTP/1.1" and, taken together,
obsoletes RFC 2616. Part 1 provides an overview of HTTP and
its associated terminology, defines the "http" and "https" Uniform
Resource Identifier (URI) schemes, defines the generic message syntax
and parsing requirements for HTTP message frames, and describes
general security concerns for implementations.
Discussion of this draft should take place on the HTTPBIS working group
mailing list (ietf-http-wg@w3.org). The current issues list is
at
and related documents (including fancy diffs) can be found at
.
The changes in this draft are summarized in .
The Hypertext Transfer Protocol (HTTP) is an application-level
request/response protocol that uses extensible semantics and MIME-like
message payloads for flexible interaction with network-based hypertext
information systems. HTTP relies upon the Uniform Resource Identifier (URI)
standard to indicate request targets and
relationships between resources.
Messages are passed in a format similar to that used by Internet mail
and the Multipurpose Internet Mail Extensions
(MIME) (see Appendix A of for the differences
between HTTP and MIME messages).
HTTP is a generic interface protocol for information systems. It is
designed to hide the details of how a service is implemented by presenting
a uniform interface to clients that is independent of the types of
resources provided. Likewise, servers do not need to be aware of each
client's purpose: an HTTP request can be considered in isolation rather
than being associated with a specific type of client or a predetermined
sequence of application steps. The result is a protocol that can be used
effectively in many different contexts and for which implementations can
evolve independently over time.
HTTP is also designed for use as an intermediation protocol for translating
communication to and from non-HTTP information systems.
HTTP proxies and gateways can provide access to alternative information
services by translating their diverse protocols into a hypertext
format that can be viewed and manipulated by clients in the same way
as HTTP services.
One consequence of HTTP flexibility is that the protocol cannot be
defined in terms of what occurs behind the interface. Instead, we
are limited to defining the syntax of communication, the intent
of received communication, and the expected behavior of recipients.
If the communication is considered in isolation, then successful
actions ought to be reflected in corresponding changes to the
observable interface provided by servers. However, since multiple
clients might act in parallel and perhaps at cross-purposes, we
cannot require that such changes be observable beyond the scope
of a single response.
This document is Part 1 of the seven-part specification of HTTP,
defining the protocol referred to as "HTTP/1.1" and obsoleting
.
Part 1 describes the architectural elements that are used or
referred to in HTTP, defines the "http" and "https" URI schemes,
describes overall network operation and connection management,
and defines HTTP message framing and forwarding requirements.
Our goal is to define all of the mechanisms necessary for HTTP message
handling that are independent of message semantics, thereby defining the
complete set of requirements for message parsers and
message-forwarding intermediaries.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in .
An implementation is not compliant if it fails to satisfy one or more
of the "MUST" or "REQUIRED" level requirements for the protocols it
implements. An implementation that satisfies all the "MUST" or "REQUIRED"
level and all the "SHOULD" level requirements for its protocols is said
to be "unconditionally compliant"; one that satisfies all the "MUST"
level requirements but not all the "SHOULD" level requirements for its
protocols is said to be "conditionally compliant".
This specification uses the Augmented Backus-Naur Form (ABNF) notation
of .
The following core rules are included by
reference, as defined in , Appendix B.1:
ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
DIGIT (decimal 0-9), DQUOTE (double quote),
HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
OCTET (any 8-bit sequence of data), SP (space),
VCHAR (any visible character),
and WSP (whitespace).
As a syntactic convention, ABNF rule names prefixed with "obs-" denote
"obsolete" grammar rules that appear for historical reasons.
The #rule extension to the ABNF rules of is used to
improve readability.
A construct "#" is defined, similar to "*", for defining comma-delimited
lists of elements. The full form is "<n>#<m>element" indicating
at least <n> and at most <m> elements, each separated by a single
comma (",") and optional whitespace (OWS,
).
Thus,
element *( OWS "," OWS element )
]]>
and:
[ 1#element ]
]]>
and for n >= 1 and m > 1:
#element => element *( OWS "," OWS element )
]]>
For compatibility with legacy list rules, recipients SHOULD accept empty
list elements. In other words, consumers would follow the list productions:
[ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
]]>
Note that empty elements do not contribute to the count of elements present,
though.
For example, given these ABNF productions:
Then these are valid values for example-list (not including the double
quotes, which are present for delimitation only):
But these values would be invalid, as at least one non-empty element is
required:
shows the collected ABNF, with the list rules
expanded as explained above.
HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
protocol elements other than the message-body
(see for tolerant applications).
This specification uses three rules to denote the use of linear
whitespace: OWS (optional whitespace), RWS (required whitespace), and
BWS ("bad" whitespace).
The OWS rule is used where zero or more linear whitespace characters might
appear. OWS SHOULD either not be produced or be produced as a single SP
character. Multiple OWS characters that occur within field-content SHOULD
be replaced with a single SP before interpreting the field value or
forwarding the message downstream.
RWS is used when at least one linear whitespace character is required to
separate field tokens. RWS SHOULD be produced as a single SP character.
Multiple RWS characters that occur within field-content SHOULD be
replaced with a single SP before interpreting the field value or
forwarding the message downstream.
BWS is used where the grammar allows optional whitespace for historical
reasons but senders SHOULD NOT produce it in messages. HTTP/1.1
recipients MUST accept such bad optional whitespace and remove it before
interpreting the field value or forwarding the message downstream.
Many HTTP/1.1 header field values consist of words (token or quoted-string)
separated by whitespace or special characters. These special characters
MUST be in a quoted string to be used within a parameter value (as defined
in ).
" / "@" / ","
/ ";" / ":" / "\" / DQUOTE / "/" / "["
/ "]" / "?" / "=" / "{" / "}"
]]>
A string of text is parsed as a single word if it is quoted using
double-quote marks.
/ obs-text
obs-text = %x80-FF
]]>
The backslash character ("\") can be used as a single-character
quoting mechanism within quoted-string constructs:
Producers SHOULD NOT escape characters that do not require escaping
(i.e., other than DQUOTE and the backslash character).
The ABNF rules below are defined in other parts:
response-header =
]]>
]]>
Pragma =
Warning =
]]>
HTTP was created for the World Wide Web architecture
and has evolved over time to support the scalability needs of a worldwide
hypertext system. Much of that architecture is reflected in the terminology
and syntax productions used to define HTTP.
HTTP is a stateless request/response protocol that operates by exchanging
messages across a reliable transport or session-layer connection. An HTTP
"client" is a program that establishes a connection to a server for the
purpose of sending one or more HTTP requests. An HTTP "server" is a
program that accepts connections in order to service HTTP requests by
sending HTTP responses.
Note that the terms client and server refer only to the roles that
these programs perform for a particular connection. The same program
might act as a client on some connections and a server on others. We use
the term "user agent" to refer to the program that initiates a request,
such as a WWW browser, editor, or spider (web-traversing robot), and
the term "origin server" to refer to the program that can originate
authoritative responses to a request. For general requirements, we use
the term "sender" to refer to whichever component sent a given message
and the term "recipient" to refer to any component that receives the
message.
Most HTTP communication consists of a retrieval request (GET) for
a representation of some resource identified by a URI. In the
simplest case, this might be accomplished via a single bidirectional
connection (===) between the user agent (UA) and the origin server (O).
UA ======================================= O
< response
]]>
A client sends an HTTP request to the server in the form of a request
message (), beginning with a method, URI, and
protocol version, followed by MIME-like header fields containing
request modifiers, client information, and payload metadata, an empty
line to indicate the end of the header section, and finally the payload
body (if any).
A server responds to the client's request by sending an HTTP response
message (), beginning with a status line that
includes the protocol version, a success or error code, and textual
reason phrase, followed by MIME-like header fields containing server
information, resource metadata, and payload metadata, an empty line to
indicate the end of the header section, and finally the payload body (if any).
The following example illustrates a typical message exchange for a
GET request on the URI "http://www.example.com/hello.txt":
client request:
server response:
A more complicated situation occurs when one or more intermediaries
are present in the request/response chain. There are three common
forms of intermediary: proxy, gateway, and tunnel. In some cases,
a single intermediary might act as an origin server, proxy, gateway,
or tunnel, switching behavior based on the nature of each request.
> > >
UA =========== A =========== B =========== C =========== O
< < < <
]]>
The figure above shows three intermediaries (A, B, and C) between the
user agent and origin server. A request or response message that
travels the whole chain will pass through four separate connections.
Some HTTP communication options
might apply only to the connection with the nearest, non-tunnel
neighbor, only to the end-points of the chain, or to all connections
along the chain. Although the diagram is linear, each participant might
be engaged in multiple, simultaneous communications. For example, B
might be receiving requests from many clients other than A, and/or
forwarding requests to servers other than C, at the same time that it
is handling A's request.
We use the terms "upstream" and "downstream" to describe various
requirements in relation to the directional flow of a message:
all messages flow from upstream to downstream.
Likewise, we use the terms "inbound" and "outbound" to refer to
directions in relation to the request path: "inbound" means toward
the origin server and "outbound" means toward the user agent.
A "proxy" is a message forwarding agent that is selected by the
client, usually via local configuration rules, to receive requests
for some type(s) of absolute URI and attempt to satisfy those
requests via translation through the HTTP interface. Some translations
are minimal, such as for proxy requests for "http" URIs, whereas
other requests might require translation to and from entirely different
application-layer protocols. Proxies are often used to group an
organization's HTTP requests through a common intermediary for the
sake of security, annotation services, or shared caching.
A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts
as a layer above some other server(s) and translates the received
requests to the underlying server's protocol. Gateways are often
used for load balancing or partitioning HTTP services across
multiple machines.
Unlike a proxy, a gateway receives requests as if it were the
origin server for the target resource; the requesting client
will not be aware that it is communicating with a gateway.
A gateway communicates with the client as if the gateway is the
origin server and thus is subject to all of the requirements on
origin servers for that connection. A gateway communicates
with inbound servers using any protocol it desires, including
private extensions to HTTP that are outside the scope of this
specification.
A "tunnel" acts as a blind relay between two connections
without changing the messages. Once active, a tunnel is not
considered a party to the HTTP communication, though the tunnel might
have been initiated by an HTTP request. A tunnel ceases to exist when
both ends of the relayed connection are closed. Tunnels are used to
extend a virtual connection through an intermediary, such as when
transport-layer security is used to establish private communication
through a shared firewall proxy.
A "cache" is a local store of previous response messages and the
subsystem that controls its message storage, retrieval, and deletion.
A cache stores cacheable responses in order to reduce the response
time and network bandwidth consumption on future, equivalent
requests. Any client or server MAY employ a cache, though a cache
cannot be used by a server while it is acting as a tunnel.
The effect of a cache is that the request/response chain is shortened
if one of the participants along the chain has a cached response
applicable to that request. The following illustrates the resulting
chain if B has a cached copy of an earlier response from O (via C)
for a request which has not been cached by UA or A.
>
UA =========== A =========== B - - - - - - C - - - - - - O
< <
]]>
A response is "cacheable" if a cache is allowed to store a copy of
the response message for use in answering subsequent requests.
Even when a response is cacheable, there might be additional
constraints placed by the client or by the origin server on when
that cached response can be used for a particular request. HTTP
requirements for cache behavior and cacheable responses are
defined in Section 2 of .
There are a wide variety of architectures and configurations
of caches and proxies deployed across the World Wide Web and
inside large organizations. These systems include national hierarchies
of proxy caches to save transoceanic bandwidth, systems that
broadcast or multicast cache entries, organizations that distribute
subsets of cached data via optical media, and so on.
HTTP systems are used in a wide variety of environments, from
corporate intranets with high-bandwidth links to long-distance
communication over low-power radio links and intermittent connectivity.
HTTP communication usually takes place over TCP/IP connections. The
default port is TCP 80 (), but other ports can be used. This does
not preclude HTTP from being implemented on top of any other protocol
on the Internet, or on other networks. HTTP only presumes a reliable
transport; any protocol that provides such guarantees can be used;
the mapping of the HTTP/1.1 request and response structures onto the
transport data units of the protocol in question is outside the scope
of this specification.
In HTTP/1.0, most implementations used a new connection for each
request/response exchange. In HTTP/1.1, a connection might be used for
one or more request/response exchanges, although connections might be
closed for a variety of reasons (see ).
HTTP uses a "<major>.<minor>" numbering scheme to indicate versions
of the protocol. The protocol versioning policy is intended to allow
the sender to indicate the format of a message and its capacity for
understanding further HTTP communication, rather than the features
obtained via that communication. No change is made to the version
number for the addition of message components which do not affect
communication behavior or which only add to extensible field values.
The <minor> number is incremented when the changes made to the
protocol add features which do not change the general message parsing
algorithm, but which might add to the message semantics and imply
additional capabilities of the sender. The <major> number is
incremented when the format of a message within the protocol is
changed. See for a fuller explanation.
The version of an HTTP message is indicated by an HTTP-Version field
in the first line of the message. HTTP-Version is case-sensitive.
Note that the major and minor numbers MUST be treated as separate
integers and that each MAY be incremented higher than a single digit.
Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
lower than HTTP/12.3. Leading zeros MUST be ignored by recipients and
MUST NOT be sent.
An application that sends a request or response message that includes
HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant
with this specification. Applications that are at least conditionally
compliant with this specification SHOULD use an HTTP-Version of
"HTTP/1.1" in their messages, and MUST do so for any message that is
not compatible with HTTP/1.0. For more details on when to send
specific HTTP-Version values, see .
The HTTP version of an application is the highest HTTP version for
which the application is at least conditionally compliant.
Proxy and gateway applications need to be careful when forwarding
messages in protocol versions different from that of the application.
Since the protocol version indicates the protocol capability of the
sender, a proxy/gateway MUST NOT send a message with a version
indicator which is greater than its actual version. If a higher
version request is received, the proxy/gateway MUST either downgrade
the request version, or respond with an error, or switch to tunnel
behavior.
Due to interoperability problems with HTTP/1.0 proxies discovered
since the publication of , caching proxies MUST, gateways
MAY, and tunnels MUST NOT upgrade the request to the highest version
they support. The proxy/gateway's response to that request MUST be in
the same major version as the request.
Note: Converting between versions of HTTP might involve modification
of header fields required or forbidden by the versions involved.
Uniform Resource Identifiers (URIs) are used
throughout HTTP as the means for identifying resources. URI references
are used to target requests, indicate redirects, and define relationships.
HTTP does not limit what a resource might be; it merely defines an interface
that can be used to interact with a resource via HTTP. More information on
the scope of URIs and resources can be found in .
This specification adopts the definitions of "URI-reference",
"absolute-URI", "relative-part", "port", "host",
"path-abempty", "path-absolute", "query", and "authority" from
. In addition, we define a partial-URI rule for
protocol elements that allow a relative URI without a fragment.
absolute-URI =
relative-part =
authority =
path-abempty =
path-absolute =
port =
query =
uri-host =
partial-URI = relative-part [ "?" query ]
]]>
Each protocol element in HTTP that allows a URI reference will indicate in
its ABNF production whether the element allows only a URI in absolute form
(absolute-URI), any relative reference (relative-ref), or some other subset
of the URI-reference grammar. Unless otherwise indicated, URI references
are parsed relative to the request target (the default base URI for both
the request and its corresponding response).
The "http" URI scheme is hereby defined for the purpose of minting
identifiers according to their association with the hierarchical
namespace governed by a potential HTTP origin server listening for
TCP connections on a given port.
The HTTP server is identified via the generic syntax's
authority component, which includes a host
identifier and optional TCP port, and the remainder of the URI is
considered to be identifying data corresponding to a resource for
which that server might provide an HTTP interface.
The host identifier within an authority component is
defined in , Section 3.2.2. If host is
provided as an IP literal or IPv4 address, then the HTTP server is any
listener on the indicated TCP port at that IP address. If host is a
registered name, then that name is considered an indirect identifier
and the recipient might use a name resolution service, such as DNS,
to find the address of a listener for that host.
The host MUST NOT be empty; if an "http" URI is received with an
empty host, then it MUST be rejected as invalid.
If the port subcomponent is empty or not given, then TCP port 80 is
assumed (the default reserved port for WWW services).
Regardless of the form of host identifier, access to that host is not
implied by the mere presence of its name or address. The host might or might
not exist and, even when it does exist, might or might not be running an
HTTP server or listening to the indicated port. The "http" URI scheme
makes use of the delegated nature of Internet names and addresses to
establish a naming authority (whatever entity has the ability to place
an HTTP server at that Internet name or address) and allows that
authority to determine which names are valid and how they might be used.
When an "http" URI is used within a context that calls for access to the
indicated resource, a client MAY attempt access by resolving
the host to an IP address, establishing a TCP connection to that address
on the indicated port, and sending an HTTP request message to the server
containing the URI's identifying data as described in .
If the server responds to that request with a non-interim HTTP response
message, as described in , then that response
is considered an authoritative answer to the client's request.
Although HTTP is independent of the transport protocol, the "http"
scheme is specific to TCP-based services because the name delegation
process depends on TCP for establishing authority.
An HTTP service based on some other underlying connection protocol
would presumably be identified using a different URI scheme, just as
the "https" scheme (below) is used for servers that require an SSL/TLS
transport layer on a connection. Other protocols might also be used to
provide access to "http" identified resources --- it is only the
authoritative interface used for mapping the namespace that is
specific to TCP.
The URI generic syntax for authority also includes a deprecated
userinfo subcomponent (, Section 3.2.1)
for including user authentication information in the URI. The userinfo
subcomponent (and its "@" delimiter) MUST NOT be used in an "http"
URI. URI reference recipients SHOULD parse for the existence of
userinfo and treat its presence as an error, likely indicating that
the deprecated subcomponent is being used to obscure the authority
for the sake of phishing attacks.
The "https" URI scheme is hereby defined for the purpose of minting
identifiers according to their association with the hierarchical
namespace governed by a potential HTTP origin server listening for
SSL/TLS-secured connections on a given TCP port.
All of the requirements listed above for the "http" scheme are also
requirements for the "https" scheme, except that a default TCP port
of 443 is assumed if the port subcomponent is empty or not given,
and the TCP connection MUST be secured for privacy through the
use of strong encryption prior to sending the first HTTP request.
Unlike the "http" scheme, responses to "https" identified requests
are never "public" and thus are ineligible for shared caching.
Their default is "private" and might be further constrained via use
of the Cache-Control header field.
Resources made available via the "https" scheme have no shared
identity with the "http" scheme even if their resource identifiers
only differ by the single "s" in the scheme name. They are
different services governed by different authorities. However,
some extensions to HTTP that apply to entire host domains, such
as the Cookie protocol, do allow one service to effect communication
with the other services based on host domain matching.
The process for authoritative access to an "https" identified
resource is defined in .
Since the "http" and "https" schemes conform to the URI generic syntax,
such URIs are normalized and compared according to the algorithm defined
in , Section 6, using the defaults
described above for each scheme.
If the port is equal to the default port for a scheme, the normal
form is to elide the port subcomponent. Likewise, an empty path
component is equivalent to an absolute path of "/", so the normal
form is to provide a path of "/" instead. The scheme and host
are case-insensitive and normally provided in lowercase; all
other components are compared in a case-sensitive manner.
Characters other than those in the "reserved" set are equivalent
to their percent-encoded octets (see , Section 2.1): the normal form is to not encode them.
For example, the following three URIs are equivalent:
This paragraph does not belong here.
If path-abempty is the empty string (i.e., there is no slash "/"
path separator following the authority), then the "http" URI
MUST be given as "/" when
used as a request-target (). If a proxy
receives a host name which is not a fully qualified domain name, it
MAY add its domain to the host name it received. If a proxy receives
a fully qualified domain name, the proxy MUST NOT change the host
name.
All HTTP/1.1 messages consist of a start-line followed by a sequence of
characters in a format similar to the Internet Message Format
: zero or more header fields (collectively
referred to as the "headers" or the "header section"), an empty line
indicating the end of the header section, and an optional message-body.
An HTTP message can either be a request from client to server or a
response from server to client. Syntactically, the two types of message
differ only in the start-line, which is either a Request-Line (for requests)
or a Status-Line (for responses), and in the algorithm for determining
the length of the message-body ().
In theory, a client could receive requests and a server could receive
responses, distinguishing them by their different start-line formats,
but in practice servers are implemented to only expect a request
(a response is interpreted as an unknown or invalid request method)
and clients are implemented to only expect a response.
Whitespace (WSP) MUST NOT be sent between the start-line and the first
header field. The presence of whitespace might be an attempt to trick a
noncompliant implementation of HTTP into ignoring that field or processing
the next line as a new request, either of which might result in security
issues when implementations within the request chain interpret the
same message differently. HTTP/1.1 servers MUST reject such a message
with a 400 (Bad Request) response.
In the interest of robustness, servers SHOULD ignore at least one
empty line received where a Request-Line is expected. In other words, if
the server is reading the protocol stream at the beginning of a
message and receives a CRLF first, it SHOULD ignore the CRLF.
Some old HTTP/1.0 client implementations generate an extra CRLF
after a POST request as a lame workaround for some early server
applications that failed to read message-body content that was
not terminated by a line-ending. An HTTP/1.1 client MUST NOT
preface or follow a request with an extra CRLF. If terminating
the request message-body with a line-ending is desired, then the
client MUST include the terminating CRLF octets as part of the
message-body length.
The normal procedure for parsing an HTTP message is to read the
start-line into a structure, read each header field into a hash
table by field name until the empty line, and then use the parsed
data to determine if a message-body is expected. If a message-body
has been indicated, then it is read as a stream until an amount
of octets equal to the message-body length is read or the connection
is closed. Care must be taken to parse an HTTP message as a sequence
of octets in an encoding that is a superset of US-ASCII. Attempting
to parse HTTP as a stream of Unicode characters in a character encoding
like UTF-16 might introduce security flaws due to the differing ways
that such parsers interpret invalid characters.
HTTP allows the set of defined header fields to be extended without
changing the protocol version (see ).
However, such fields might not be recognized by a downstream recipient
and might be stripped by non-transparent intermediaries.
Unrecognized header fields MUST be forwarded by transparent proxies
and SHOULD be ignored by a recipient.
Each HTTP header field consists of a case-insensitive field name
followed by a colon (":"), optional whitespace, and the field value.
No whitespace is allowed between the header field name and colon. For
security reasons, any request message received containing such whitespace
MUST be rejected with a response code of 400 (Bad Request). A proxy
MUST remove any such whitespace from a response message before
forwarding the message downstream.
A field value MAY be preceded by optional whitespace (OWS); a single SP is
preferred. The field value does not include any leading or trailing white
space: OWS occurring before the first non-whitespace character of the
field value or after the last non-whitespace character of the field value
is ignored and SHOULD be removed before further processing (as this does
not change the meaning of the header field).
The order in which header fields with differing field names are
received is not significant. However, it is "good practice" to send
header fields that contain control data first, such as Host on
requests and Date on responses, so that implementations can decide
when not to handle a message as early as possible. A server MUST
wait until the entire header section is received before interpreting
a request message, since later header fields might include conditionals,
authentication credentials, or deliberately misleading duplicate
header fields that would impact request processing.
Multiple header fields with the same field name MUST NOT be
sent in a message unless the entire field value for that
header field is defined as a comma-separated list [i.e., #(values)].
Multiple header fields with the same field name can be combined into
one "field-name: field-value" pair, without changing the semantics of the
message, by appending each subsequent field value to the combined
field value in order, separated by a comma. The order in which
header fields with the same field name are received is therefore
significant to the interpretation of the combined field value;
a proxy MUST NOT change the order of these field values when
forwarding a message.
Note: The "Set-Cookie" header field as implemented in
practice (as opposed to how it is specified in )
can occur multiple times, but does not use the list syntax, and thus cannot
be combined into a single line. (See Appendix A.2.3 of
for details.) Also note that the Set-Cookie2 header field specified in
does not share this problem.
Historically, HTTP header field values could be extended over multiple
lines by preceding each extra line with at least one space or horizontal
tab character (line folding). This specification deprecates such line
folding except within the message/http media type
().
HTTP/1.1 senders MUST NOT produce messages that include line folding
(i.e., that contain any field-content that matches the obs-fold rule) unless
the message is intended for packaging within the message/http media type.
HTTP/1.1 recipients SHOULD accept line folding and replace any embedded
obs-fold whitespace with a single SP prior to interpreting the field value
or forwarding the message downstream.
Historically, HTTP has allowed field content with text in the ISO-8859-1
character encoding and supported other
character sets only through use of encoding.
In practice, most HTTP header field values use only a subset of the
US-ASCII character encoding . Newly defined
header fields SHOULD limit their field values to US-ASCII characters.
Recipients SHOULD treat other (obs-text) octets in field content as
opaque data.
Comments can be included in some HTTP header fields by surrounding
the comment text with parentheses. Comments are only allowed in
fields containing "comment" as part of their field value definition.
/ obs-text
]]>
The backslash character ("\") can be used as a single-character
quoting mechanism within comment constructs:
Producers SHOULD NOT escape characters that do not require escaping
(i.e., other than the backslash character "\" and the parentheses "(" and
")").
The message-body (if any) of an HTTP message is used to carry the
payload body associated with the request or response.
The message-body differs from the payload body only when a transfer-coding
has been applied, as indicated by the Transfer-Encoding header field (). When one or more transfer-codings are
applied to a payload in order to form the message-body, the
Transfer-Encoding header field MUST contain the list of
transfer-codings applied. Transfer-Encoding is a property of the message,
not of the payload, and thus MAY be added or removed by any implementation
along the request/response chain under the constraints found in
.
The rules for when a message-body is allowed in a message differ for
requests and responses.
The presence of a message-body in a request is signaled by the
inclusion of a Content-Length or Transfer-Encoding header field in
the request's header fields, even if the request method does not
define any use for a message-body. This allows the request
message framing algorithm to be independent of method semantics.
For response messages, whether or not a message-body is included with
a message is dependent on both the request method and the response
status code ().
Responses to the HEAD request method never include a message-body
because the associated response header fields (e.g., Transfer-Encoding,
Content-Length, etc.) only indicate what their values would have been
if the method had been GET. All 1xx (Informational), 204 (No Content),
and 304 (Not Modified) responses MUST NOT include a message-body.
All other responses do include a message-body, although the body
MAY be of zero length.
The length of the message-body is determined by one of the following
(in order of precedence):
Any response to a HEAD request and any response with a status
code of 100-199, 204, or 304 is always terminated by the first
empty line after the header fields, regardless of the header
fields present in the message, and thus cannot contain a message-body.
If a Transfer-Encoding header field ()
is present and the "chunked" transfer-coding ()
is the final encoding, the message-body length is determined by reading
and decoding the chunked data until the transfer-coding indicates the
data is complete.
If a Transfer-Encoding header field is present in a response and the
"chunked" transfer-coding is not the final encoding, the message-body
length is determined by reading the connection until it is closed by
the server.
If a Transfer-Encoding header field is present in a request and the
"chunked" transfer-coding is not the final encoding, the message-body
length cannot be determined reliably; the server MUST respond with
the 400 (Bad Request) status code and then close the connection.
If a message is received with both a Transfer-Encoding header field and a
Content-Length header field, the Transfer-Encoding overrides the Content-Length.
Such a message might indicate an attempt to perform request or response
smuggling (bypass of security-related checks on message routing or content)
and thus ought to be handled as an error. The provided Content-Length MUST
be removed, prior to forwarding the message downstream, or replaced with
the real message-body length after the transfer-coding is decoded.
If a message is received without Transfer-Encoding and with either
multiple Content-Length header fields or a single Content-Length header
field with an invalid value, then the message framing is invalid and
MUST be treated as an error to prevent request or response smuggling.
If this is a request message, the server MUST respond with
a 400 (Bad Request) status code and then close the connection.
If this is a response message received by a proxy or gateway, the proxy
or gateway MUST discard the received response, send a 502 (Bad Gateway)
status code as its downstream response, and then close the connection.
If this is a response message received by a user-agent, it SHOULD be
treated as an error by discarding the message and closing the connection.
If a valid Content-Length header field ()
is present without Transfer-Encoding, its decimal value defines the
message-body length in octets. If the actual number of octets sent in
the message is less than the indicated Content-Length, the recipient
MUST consider the message to be incomplete and treat the connection
as no longer usable.
If the actual number of octets sent in the message is more than the indicated
Content-Length, the recipient MUST only process the message-body up to the
field value's number of octets; the remainder of the message MUST either
be discarded or treated as the next message in a pipeline. For the sake of
robustness, a user-agent MAY attempt to detect and correct such an error
in message framing if it is parsing the response to the last request on
on a connection and the connection has been closed by the server.
If this is a request message and none of the above are true, then the
message-body length is zero (no message-body is present).
Otherwise, this is a response message without a declared message-body
length, so the message-body length is determined by the number of octets
received prior to the server closing the connection.
Since there is no way to distinguish a successfully completed,
close-delimited message from a partially-received message interrupted
by network failure, implementations SHOULD use encoding or
length-delimited messages whenever possible. The close-delimiting
feature exists primarily for backwards compatibility with HTTP/1.0.
A server MAY reject a request that contains a message-body but
not a Content-Length by responding with 411 (Length Required).
Unless a transfer-coding other than "chunked" has been applied,
a client that sends a request containing a message-body SHOULD
use a valid Content-Length header field if the message-body length
is known in advance, rather than the "chunked" encoding, since some
existing services respond to "chunked" with a 411 (Length Required)
status code even though they understand the chunked encoding. This
is typically because such services are implemented via a gateway that
requires a content-length in advance of being called and the server
is unable or unwilling to buffer the entire request before processing.
A client that sends a request containing a message-body MUST include a
valid Content-Length header field if it does not know the server will
handle HTTP/1.1 (or later) requests; such knowledge can be in the form
of specific user configuration or by remembering the version of a prior
received response.
Request messages that are prematurely terminated, possibly due to a
cancelled connection or a server-imposed time-out exception, MUST
result in closure of the connection; sending an HTTP/1.1 error response
prior to closing the connection is OPTIONAL.
Response messages that are prematurely terminated, usually by closure
of the connection prior to receiving the expected number of octets or by
failure to decode a transfer-encoded message-body, MUST be recorded
as incomplete. A user agent MUST NOT render an incomplete response
message-body as if it were complete (i.e., some indication must be given
to the user that an error occurred). Cache requirements for incomplete
responses are defined in Section 2.1.1 of .
A server MUST read the entire request message-body or close
the connection after sending its response, since otherwise the
remaining data on a persistent connection would be misinterpreted
as the next request. Likewise,
a client MUST read the entire response message-body if it intends
to reuse the same connection for a subsequent request. Pipelining
multiple requests on a connection is described in .
There are a few header fields which have general applicability for
both request and response messages, but which do not apply to the
payload being transferred. These header fields apply only to the
message being transmitted.
General-header field names can be extended reliably only in
combination with a change in the protocol version. However, new or
experimental header fields might be given the semantics of general
header fields if all parties in the communication recognize them to
be general-header fields.
A request message from a client to a server includes, within the
first line of that message, the method to be applied to the resource,
the identifier of the resource, and the protocol version in use.
The Request-Line begins with a method token, followed by the
request-target and the protocol version, and ending with CRLF. The
elements are separated by SP characters. No CR or LF is allowed
except in the final CRLF sequence.
The Method token indicates the method to be performed on the
resource identified by the request-target. The method is case-sensitive.
The request-target identifies the resource upon which to apply the request.
The four options for request-target are dependent on the nature of the
request.
The asterisk "*" ("asterisk form") means that the request does not apply to a
particular resource, but to the server itself, and is only allowed
when the method used does not necessarily apply to a resource. One
example would be
The absolute-URI form is REQUIRED when the request is being made to a
proxy. The proxy is requested to forward the request or service it
from a valid cache, and return the response. Note that the proxy MAY
forward the request on to another proxy or directly to the server
specified by the absolute-URI. In order to avoid request loops, a
proxy MUST be able to recognize all of its server names, including
any aliases, local variations, and the numeric IP address. An example
Request-Line would be:
To allow for transition to absolute-URIs in all requests in future
versions of HTTP, all HTTP/1.1 servers MUST accept the absolute-URI
form in requests, even though HTTP/1.1 clients will only generate
them in requests to proxies.
The authority form is only used by the CONNECT method (Section 7.9 of ).
The most common form of request-target is that used to identify a
resource on an origin server or gateway ("path-absolute form"). In this case the absolute
path of the URI MUST be transmitted (see , path-absolute) as
the request-target, and the network location of the URI (authority) MUST
be transmitted in a Host header field. For example, a client wishing
to retrieve the resource above directly from the origin server would
create a TCP connection to port 80 of the host "www.example.org" and send
the lines:
followed by the remainder of the Request. Note that the absolute path
cannot be empty; if none is present in the original URI, it MUST be
given as "/" (the server root).
If a proxy receives a request without any path in the request-target and
the method specified is capable of supporting the asterisk form of
request-target, then the last proxy on the request chain MUST forward the
request with "*" as the final request-target.
For example, the request
would be forwarded by the proxy as
after connecting to port 8001 of host "www.example.org".
The request-target is transmitted in the format specified in
. If the request-target is percent-encoded
(, Section 2.1), the origin server
MUST decode the request-target in order to
properly interpret the request. Servers SHOULD respond to invalid
request-targets with an appropriate status code.
A transparent proxy MUST NOT rewrite the "path-absolute" part of the
received request-target when forwarding it to the next inbound server,
except as noted above to replace a null path-absolute with "/" or "*".
Note: The "no rewrite" rule prevents the proxy from changing the
meaning of the request when the origin server is improperly using
a non-reserved URI character for a reserved purpose. Implementors
need to be aware that some pre-HTTP/1.1 proxies have been known to
rewrite the request-target.
HTTP does not place a pre-defined limit on the length of a request-target.
A server MUST be prepared to receive URIs of unbounded length and
respond with the 414 (URI Too Long) status code if the received
request-target would be longer than the server wishes to handle
(see Section 8.4.15 of ).
Various ad-hoc limitations on request-target length are found in practice.
It is RECOMMENDED that all HTTP senders and recipients support
request-target lengths of 8000 or more octets.
Note: Fragments (, Section 3.5)
are not part of the request-target and thus will not be transmitted
in an HTTP request.
The exact resource identified by an Internet request is determined by
examining both the request-target and the Host header field.
An origin server that does not allow resources to differ by the
requested host MAY ignore the Host header field value when
determining the resource identified by an HTTP/1.1 request. (But see
for other requirements on Host support in HTTP/1.1.)
An origin server that does differentiate resources based on the host
requested (sometimes referred to as virtual hosts or vanity host
names) MUST use the following rules for determining the requested
resource on an HTTP/1.1 request:
If request-target is an absolute-URI, the host is part of the
request-target. Any Host header field value in the request MUST be
ignored.If the request-target is not an absolute-URI, and the request includes
a Host header field, the host is determined by the Host header
field value.If the host as determined by rule 1 or 2 is not a valid host on
the server, the response MUST be a 400 (Bad Request) error message.
Recipients of an HTTP/1.0 request that lacks a Host header field MAY
attempt to use heuristics (e.g., examination of the URI path for
something unique to a particular host) in order to determine what
exact resource is being requested.
HTTP requests often do not carry the absolute URI (, Section 4.3)
for the target resource; instead, the URI needs to be inferred from the
request-target, Host header field, and connection context. The result of
this process is called the "effective request URI". The "target resource"
is the resource identified by the effective request URI.
If the request-target is an absolute-URI, then the effective request URI is
the request-target.
If the request-target uses the path-absolute form or the asterisk form,
and the Host header field is present, then the effective request URI is
constructed by concatenating
the scheme name: "http" if the request was received over an insecure
TCP connection, or "https" when received over a SSL/TLS-secured TCP
connection,
the character sequence "://",
the authority component, as specified in the Host header field
(), and
the request-target obtained from the Request-Line, unless the
request-target is just the asterisk "*".
If the request-target uses the path-absolute form or the asterisk form,
and the Host header field is not present, then the effective request URI is
undefined.
Otherwise, when request-target uses the authority form, the effective
request URI is undefined.
Example 1: the effective request URI for the message
(received over an insecure TCP connection) is "http", plus "://", plus the
authority component "www.example.org:8080", plus the request-target
"/pub/WWW/TheProject.html", thus
"http://www.example.org:8080/pub/WWW/TheProject.html".
Example 2: the effective request URI for the message
(received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
authority component "www.example.org", thus "https://www.example.org".
Effective request URIs are compared using the rules described in
, except that empty path components MUST NOT
be treated as equivalent to an absolute path of "/".
After receiving and interpreting a request message, a server responds
with an HTTP response message.
The first line of a Response message is the Status-Line, consisting
of the protocol version followed by a numeric status code and its
associated textual phrase, with each element separated by SP
characters. No CR or LF is allowed except in the final CRLF sequence.
The Status-Code element is a 3-digit integer result code of the
attempt to understand and satisfy the request. These codes are fully
defined in Section 8 of . The Reason Phrase exists for the sole
purpose of providing a textual description associated with the numeric
status code, out of deference to earlier Internet application protocols
that were more frequently used with interactive text clients.
A client SHOULD ignore the content of the Reason Phrase.
The first digit of the Status-Code defines the class of response. The
last two digits do not have any categorization role. There are 5
values for the first digit:
1xx: Informational - Request received, continuing process
2xx: Success - The action was successfully received,
understood, and accepted
3xx: Redirection - Further action must be taken in order to
complete the request
4xx: Client Error - The request contains bad syntax or cannot
be fulfilled
5xx: Server Error - The server failed to fulfill an apparently
valid request
HTTP applications have historically allowed three different formats
for date/time stamps. However, the preferred format is a fixed-length subset
of that defined by :
The other formats are described here only for compatibility with obsolete
implementations.
HTTP/1.1 clients and servers that parse a date value MUST accept
all three formats (for compatibility with HTTP/1.0), though they MUST
only generate the RFC 1123 format for representing HTTP-date values
in header fields. See for further information.
All HTTP date/time stamps MUST be represented in Greenwich Mean Time
(GMT), without exception. For the purposes of HTTP, GMT is exactly
equal to UTC (Coordinated Universal Time). This is indicated in the
first two formats by the inclusion of "GMT" as the three-letter
abbreviation for time zone, and MUST be assumed when reading the
asctime format. HTTP-date is case sensitive and MUST NOT include
additional whitespace beyond that specifically included as SP in the
grammar.
Preferred format:
The semantics of day-name, day,
month, year, and time-of-day are the
same as those defined for the RFC 5322 constructs
with the corresponding name (, Section 3.3).
Obsolete formats:
Note: Recipients of date values are encouraged to be robust in
accepting date values that might have been sent by non-HTTP
applications, as is sometimes the case when retrieving or posting
messages via proxies/gateways to SMTP or NNTP.
Note: HTTP requirements for the date/time stamp format apply only
to their usage within the protocol stream. Clients and servers are
not required to use these formats for user presentation, request
logging, etc.
Transfer-coding values are used to indicate an encoding
transformation that has been, can be, or might need to be applied to a
payload body in order to ensure "safe transport" through the network.
This differs from a content coding in that the transfer-coding is a
property of the message rather than a property of the representation
that is being transferred.
Parameters are in the form of attribute/value pairs.
All transfer-coding values are case-insensitive. HTTP/1.1 uses
transfer-coding values in the TE header field () and in
the Transfer-Encoding header field ().
Transfer-codings are analogous to the Content-Transfer-Encoding values of
MIME, which were designed to enable safe transport of binary data over a
7-bit transport service (, Section 6).
However, safe transport
has a different focus for an 8bit-clean transfer protocol. In HTTP,
the only unsafe characteristic of message-bodies is the difficulty in
determining the exact message body length (),
or the desire to encrypt data over a shared transport.
A server that receives a request message with a transfer-coding it does
not understand SHOULD respond with 501 (Not Implemented) and then
close the connection. A server MUST NOT send transfer-codings to an HTTP/1.0
client.
The chunked encoding modifies the body of a message in order to
transfer it as a series of chunks, each with its own size indicator,
followed by an OPTIONAL trailer containing header fields. This
allows dynamically produced content to be transferred along with the
information necessary for the recipient to verify that it has
received the full message.
/ obs-text
]]>
The chunk-size field is a string of hex digits indicating the size of
the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
zero, followed by the trailer, which is terminated by an empty line.
The trailer allows the sender to include additional HTTP header
fields at the end of the message. The Trailer header field can be
used to indicate which header fields are included in a trailer (see
).
A server using chunked transfer-coding in a response MUST NOT use the
trailer for any header fields unless at least one of the following is
true:
the request included a TE header field that indicates "trailers" is
acceptable in the transfer-coding of the response, as described in
; or,the trailer fields consist entirely of optional metadata, and the
recipient could use the message (in a manner acceptable to the server where
the field originated) without receiving it. In other words, the server that
generated the header (often but not always the origin server) is willing to
accept the possibility that the trailer fields might be silently discarded
along the path to the client.
This requirement prevents an interoperability failure when the
message is being received by an HTTP/1.1 (or later) proxy and
forwarded to an HTTP/1.0 recipient. It avoids a situation where
compliance with the protocol would have necessitated a possibly
infinite buffer on the proxy.
A process for decoding the "chunked" transfer-coding
can be represented in pseudo-code as:
0) {
read chunk-data and CRLF
append chunk-data to decoded-body
length := length + chunk-size
read chunk-size and CRLF
}
read header-field
while (header-field not empty) {
append header-field to existing header fields
read header-field
}
Content-Length := length
Remove "chunked" from Transfer-Encoding
]]>
All HTTP/1.1 applications MUST be able to receive and decode the
"chunked" transfer-coding and MUST ignore chunk-ext extensions
they do not understand.
Since "chunked" is the only transfer-coding required to be understood
by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
on a persistent connection. Whenever a transfer-coding is applied to
a payload body in a request, the final transfer-coding applied MUST
be "chunked". If a transfer-coding is applied to a response payload
body, then either the final transfer-coding applied MUST be "chunked"
or the message MUST be terminated by closing the connection. When the
"chunked" transfer-coding is used, it MUST be the last transfer-coding
applied to form the message-body. The "chunked" transfer-coding MUST NOT
be applied more than once in a message-body.
The codings defined below can be used to compress the payload of a
message.
Note: Use of program names for the identification of encoding formats
is not desirable and is discouraged for future encodings. Their
use here is representative of historical practice, not good
design.
Note: For compatibility with previous implementations of HTTP,
applications SHOULD consider "x-gzip" and "x-compress" to be
equivalent to "gzip" and "compress" respectively.
The "compress" format is produced by the common UNIX file compression
program "compress". This format is an adaptive Lempel-Ziv-Welch
coding (LZW).
The "deflate" format is defined as the "deflate" compression mechanism
(described in ) used inside the "zlib"
data format ().
Note: Some incorrect implementations send the "deflate"
compressed data without the zlib wrapper.
The "gzip" format is produced by the file compression program
"gzip" (GNU zip), as described in . This format is a
Lempel-Ziv coding (LZ77) with a 32 bit CRC.
The HTTP Transfer Coding Registry defines the name space for the transfer
coding names.
Registrations MUST include the following fields:
NameDescriptionPointer to specification text
Names of transfer codings MUST NOT overlap with names of content codings
(Section 2.2 of ), unless the encoding transformation is identical (as it
is the case for the compression codings defined in
).
Values to be added to this name space require a specification
(see "Specification Required" in Section 4.1 of ), and MUST
conform to the purpose of transfer coding defined in this section.
The registry itself is maintained at
.
Product tokens are used to allow communicating applications to
identify themselves by software name and version. Most fields using
product tokens also allow sub-products which form a significant part
of the application to be listed, separated by whitespace. By
convention, the products are listed in order of their significance
for identifying the application.
Examples:
Product tokens SHOULD be short and to the point. They MUST NOT be
used for advertising or other non-essential information. Although any
token character MAY appear in a product-version, this token SHOULD
only be used for a version identifier (i.e., successive versions of
the same product SHOULD only differ in the product-version portion of
the product value).
Both transfer codings (TE request header field, )
and content negotiation (Section 5 of ) use short "floating point"
numbers to indicate the relative importance ("weight") of various
negotiable parameters. A weight is normalized to a real number in
the range 0 through 1, where 0 is the minimum and 1 the maximum
value. If a parameter has a quality value of 0, then content with
this parameter is "not acceptable" for the client. HTTP/1.1
applications MUST NOT generate more than three digits after the
decimal point. User configuration of these values SHOULD also be
limited in this fashion.
Note: "Quality values" is a misnomer, since these values merely represent
relative degradation in desired quality.
Prior to persistent connections, a separate TCP connection was
established to fetch each URL, increasing the load on HTTP servers
and causing congestion on the Internet. The use of inline images and
other associated data often requires a client to make multiple
requests of the same server in a short amount of time. Analysis of
these performance problems and results from a prototype
implementation are available . Implementation experience and
measurements of actual HTTP/1.1 implementations show good
results . Alternatives have also been explored, for example,
T/TCP .
Persistent HTTP connections have a number of advantages:
By opening and closing fewer TCP connections, CPU time is saved
in routers and hosts (clients, servers, proxies, gateways,
tunnels, or caches), and memory used for TCP protocol control
blocks can be saved in hosts.
HTTP requests and responses can be pipelined on a connection.
Pipelining allows a client to make multiple requests without
waiting for each response, allowing a single TCP connection to
be used much more efficiently, with much lower elapsed time.
Network congestion is reduced by reducing the number of packets
caused by TCP opens, and by allowing TCP sufficient time to
determine the congestion state of the network.
Latency on subsequent requests is reduced since there is no time
spent in TCP's connection opening handshake.
HTTP can evolve more gracefully, since errors can be reported
without the penalty of closing the TCP connection. Clients using
future versions of HTTP might optimistically try a new feature,
but if communicating with an older server, retry with old
semantics after an error is reported.
HTTP implementations SHOULD implement persistent connections.
A significant difference between HTTP/1.1 and earlier versions of
HTTP is that persistent connections are the default behavior of any
HTTP connection. That is, unless otherwise indicated, the client
SHOULD assume that the server will maintain a persistent connection,
even after error responses from the server.
Persistent connections provide a mechanism by which a client and a
server can signal the close of a TCP connection. This signaling takes
place using the Connection header field (). Once a close
has been signaled, the client MUST NOT send any more requests on that
connection.
An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
maintain a persistent connection unless a Connection header field including
the connection-token "close" was sent in the request. If the server
chooses to close the connection immediately after sending the
response, it SHOULD send a Connection header field including the
connection-token "close".
An HTTP/1.1 client MAY expect a connection to remain open, but would
decide to keep it open based on whether the response from a server
contains a Connection header field with the connection-token close. In case
the client does not want to maintain a connection for more than that
request, it SHOULD send a Connection header field including the
connection-token close.
If either the client or the server sends the close token in the
Connection header field, that request becomes the last one for the
connection.
Clients and servers SHOULD NOT assume that a persistent connection is
maintained for HTTP versions less than 1.1 unless it is explicitly
signaled. See for more information on backward
compatibility with HTTP/1.0 clients.
In order to remain persistent, all messages on the connection MUST
have a self-defined message length (i.e., one not defined by closure
of the connection), as described in .
A client that supports persistent connections MAY "pipeline" its
requests (i.e., send multiple requests without waiting for each
response). A server MUST send its responses to those requests in the
same order that the requests were received.
Clients which assume persistent connections and pipeline immediately
after connection establishment SHOULD be prepared to retry their
connection if the first pipelined attempt fails. If a client does
such a retry, it MUST NOT pipeline before it knows the connection is
persistent. Clients MUST also be prepared to resend their requests if
the server closes the connection before sending all of the
corresponding responses.
Clients SHOULD NOT pipeline requests using non-idempotent methods or
non-idempotent sequences of methods (see Section 7.1.2 of ). Otherwise, a
premature termination of the transport connection could lead to
indeterminate results. A client wishing to send a non-idempotent
request SHOULD wait to send that request until it has received the
response status line for the previous request.
It is especially important that proxies correctly implement the
properties of the Connection header field as specified in .
The proxy server MUST signal persistent connections separately with
its clients and the origin servers (or other proxy servers) that it
connects to. Each persistent connection applies to only one transport
link.
A proxy server MUST NOT establish a HTTP/1.1 persistent connection
with an HTTP/1.0 client (but see Section 19.7.1 of
for information and discussion of the problems with the Keep-Alive header field
implemented by many HTTP/1.0 clients).
For the purpose of defining the behavior of caches and non-caching
proxies, we divide HTTP header fields into two categories:
End-to-end header fields, which are transmitted to the ultimate
recipient of a request or response. End-to-end header fields in
responses MUST be stored as part of a cache entry and MUST be
transmitted in any response formed from a cache entry.Hop-by-hop header fields, which are meaningful only for a single
transport-level connection, and are not stored by caches or
forwarded by proxies.
The following HTTP/1.1 header fields are hop-by-hop header fields:
ConnectionKeep-AliveProxy-AuthenticateProxy-AuthorizationTETrailerTransfer-EncodingUpgrade
All other header fields defined by HTTP/1.1 are end-to-end header fields.
Other hop-by-hop header fields MUST be listed in a Connection header field
().
Some features of HTTP/1.1, such as Digest Authentication, depend on the
value of certain end-to-end header fields. A transparent proxy SHOULD NOT
modify an end-to-end header field unless the definition of that header field requires
or specifically allows that.
A transparent proxy MUST NOT modify any of the following fields in a
request or response, and it MUST NOT add any of these fields if not
already present:
Content-LocationContent-MD5ETagLast-Modified
A transparent proxy MUST NOT modify any of the following fields in a
response:
Expires
but it MAY add any of these fields if not already present. If an
Expires header field is added, it MUST be given a field-value identical to
that of the Date header field in that response.
A proxy MUST NOT modify or add any of the following fields in a
message that contains the no-transform cache-control directive, or in
any request:
Content-EncodingContent-RangeContent-Type
A non-transparent proxy MAY modify or add these fields to a message
that does not include no-transform, but if it does so, it MUST add a
Warning 214 (Transformation applied) if one does not already appear
in the message (see Section 3.6 of ).
Warning: Unnecessary modification of end-to-end header fields might
cause authentication failures if stronger authentication
mechanisms are introduced in later versions of HTTP. Such
authentication mechanisms MAY rely on the values of header fields
not listed here.
A transparent proxy MUST preserve the message payload (),
though it MAY change the message-body through application or removal
of a transfer-coding ().
Servers will usually have some time-out value beyond which they will
no longer maintain an inactive connection. Proxy servers might make
this a higher value since it is likely that the client will be making
more connections through the same server. The use of persistent
connections places no requirements on the length (or existence) of
this time-out for either the client or the server.
When a client or server wishes to time-out it SHOULD issue a graceful
close on the transport connection. Clients and servers SHOULD both
constantly watch for the other side of the transport close, and
respond to it as appropriate. If a client or server does not detect
the other side's close promptly it could cause unnecessary resource
drain on the network.
A client, server, or proxy MAY close the transport connection at any
time. For example, a client might have started to send a new request
at the same time that the server has decided to close the "idle"
connection. From the server's point of view, the connection is being
closed while it was idle, but from the client's point of view, a
request is in progress.
This means that clients, servers, and proxies MUST be able to recover
from asynchronous close events. Client software SHOULD reopen the
transport connection and retransmit the aborted sequence of requests
without user interaction so long as the request sequence is
idempotent (see Section 7.1.2 of ). Non-idempotent methods or sequences
MUST NOT be automatically retried, although user agents MAY offer a
human operator the choice of retrying the request(s). Confirmation by
user-agent software with semantic understanding of the application
MAY substitute for user confirmation. The automatic retry SHOULD NOT
be repeated if the second sequence of requests fails.
Servers SHOULD always respond to at least one request per connection,
if at all possible. Servers SHOULD NOT close a connection in the
middle of transmitting a response, unless a network or client failure
is suspected.
Clients (including proxies) SHOULD limit the number of simultaneous
connections that they maintain to a given server (including proxies).
Previous revisions of HTTP gave a specific number of connections as a
ceiling, but this was found to be impractical for many applications. As a
result, this specification does not mandate a particular maximum number of
connections, but instead encourages clients to be conservative when opening
multiple connections.
In particular, while using multiple connections avoids the "head-of-line
blocking" problem (whereby a request that takes significant server-side
processing and/or has a large payload can block subsequent requests on the
same connection), each connection used consumes server resources (sometimes
significantly), and furthermore using multiple connections can cause
undesirable side effects in congested networks.
Note that servers might reject traffic that they deem abusive, including an
excessive number of connections from a client.
HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
flow control mechanisms to resolve temporary overloads, rather than
terminating connections with the expectation that clients will retry.
The latter technique can exacerbate network congestion.
An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
the network connection for an error status code while it is transmitting
the request. If the client sees an error status code, it SHOULD
immediately cease transmitting the body. If the body is being sent
using a "chunked" encoding (), a zero length chunk and
empty trailer MAY be used to prematurely mark the end of the message.
If the body was preceded by a Content-Length header field, the client MUST
close the connection.
The purpose of the 100 (Continue) status code (see Section 8.1.1 of ) is to
allow a client that is sending a request message with a request body
to determine if the origin server is willing to accept the request
(based on the request header fields) before the client sends the request
body. In some cases, it might either be inappropriate or highly
inefficient for the client to send the body if the server will reject
the message without looking at the body.
Requirements for HTTP/1.1 clients:
If a client will wait for a 100 (Continue) response before
sending the request body, it MUST send an Expect request-header
field (Section 9.2 of ) with the "100-continue" expectation.
A client MUST NOT send an Expect request-header field (Section 9.2 of )
with the "100-continue" expectation if it does not intend
to send a request body.
Because of the presence of older implementations, the protocol allows
ambiguous situations in which a client might send "Expect: 100-continue"
without receiving either a 417 (Expectation Failed)
or a 100 (Continue) status code. Therefore, when a client sends this
header field to an origin server (possibly via a proxy) from which it
has never seen a 100 (Continue) status code, the client SHOULD NOT
wait for an indefinite period before sending the request body.
Requirements for HTTP/1.1 origin servers:
Upon receiving a request which includes an Expect request-header
field with the "100-continue" expectation, an origin server MUST
either respond with 100 (Continue) status code and continue to read
from the input stream, or respond with a final status code. The
origin server MUST NOT wait for the request body before sending
the 100 (Continue) response. If it responds with a final status
code, it MAY close the transport connection or it MAY continue
to read and discard the rest of the request. It MUST NOT
perform the requested method if it returns a final status code.
An origin server SHOULD NOT send a 100 (Continue) response if
the request message does not include an Expect request-header
field with the "100-continue" expectation, and MUST NOT send a
100 (Continue) response if such a request comes from an HTTP/1.0
(or earlier) client. There is an exception to this rule: for
compatibility with , a server MAY send a 100 (Continue)
status code in response to an HTTP/1.1 PUT or POST request that does
not include an Expect request-header field with the "100-continue"
expectation. This exception, the purpose of which is
to minimize any client processing delays associated with an
undeclared wait for 100 (Continue) status code, applies only to
HTTP/1.1 requests, and not to requests with any other HTTP-version
value.
An origin server MAY omit a 100 (Continue) response if it has
already received some or all of the request body for the
corresponding request.
An origin server that sends a 100 (Continue) response MUST
ultimately send a final status code, once the request body is
received and processed, unless it terminates the transport
connection prematurely.
If an origin server receives a request that does not include an
Expect request-header field with the "100-continue" expectation,
the request includes a request body, and the server responds
with a final status code before reading the entire request body
from the transport connection, then the server SHOULD NOT close
the transport connection until it has read the entire request,
or until the client closes the connection. Otherwise, the client
might not reliably receive the response message. However, this
requirement is not be construed as preventing a server from
defending itself against denial-of-service attacks, or from
badly broken client implementations.
Requirements for HTTP/1.1 proxies:
If a proxy receives a request that includes an Expect request-header
field with the "100-continue" expectation, and the proxy
either knows that the next-hop server complies with HTTP/1.1 or
higher, or does not know the HTTP version of the next-hop
server, it MUST forward the request, including the Expect header
field.
If the proxy knows that the version of the next-hop server is
HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
respond with a 417 (Expectation Failed) status code.
Proxies SHOULD maintain a cache recording the HTTP version
numbers received from recently-referenced next-hop servers.
A proxy MUST NOT forward a 100 (Continue) response if the
request message was received from an HTTP/1.0 (or earlier)
client and did not include an Expect request-header field with
the "100-continue" expectation. This requirement overrides the
general rule for forwarding of 1xx responses (see Section 8.1 of ).
If an HTTP/1.1 client sends a request which includes a request body,
but which does not include an Expect request-header field with the
"100-continue" expectation, and if the client is not directly
connected to an HTTP/1.1 origin server, and if the client sees the
connection close before receiving a status line from the server, the
client SHOULD retry the request. If the client does retry this
request, it MAY use the following "binary exponential backoff"
algorithm to be assured of obtaining a reliable response:
Initiate a new connection to the server
Transmit the request-header fields
Initialize a variable R to the estimated round-trip time to the
server (e.g., based on the time it took to establish the
connection), or to a constant value of 5 seconds if the round-trip
time is not available.
Compute T = R * (2**N), where N is the number of previous
retries of this request.
Wait either for an error response from the server, or for T
seconds (whichever comes first)
If no error response is received, after T seconds transmit the
body of the request.
If client sees that the connection is closed prematurely,
repeat from step 1 until the request is accepted, an error
response is received, or the user becomes impatient and
terminates the retry process.
If at any point an error status code is received, the client
SHOULD NOT continue andSHOULD close the connection if it has not completed sending the
request message.describe why aliases like webcal are harmful.Configured to use HTTP to proxy HTTP or other protocols.Interception of HTTP traffic for initiating access control.Profiles of HTTP defined by other protocol.
Extensions of HTTP like WebDAV.Instructions on composing HTTP requests via hypertext formats.
This section defines the syntax and semantics of HTTP/1.1 header fields
related to message framing and transport protocols.
The "Connection" general-header field allows the sender to specify
options that are desired for that particular connection and MUST NOT
be communicated by proxies over further connections.
The Connection header field's value has the following grammar:
HTTP/1.1 proxies MUST parse the Connection header field before a
message is forwarded and, for each connection-token in this field,
remove any header field(s) from the message with the same name as the
connection-token. Connection options are signaled by the presence of
a connection-token in the Connection header field, not by any
corresponding additional header field(s), since the additional header
field might not be sent if there are no parameters associated with that
connection option.
Message header fields listed in the Connection header field MUST NOT include
end-to-end header fields, such as Cache-Control.
HTTP/1.1 defines the "close" connection option for the sender to
signal that the connection will be closed after completion of the
response. For example,
in either the request or the response header fields indicates that
the connection SHOULD NOT be considered "persistent" ()
after the current request/response is complete.
An HTTP/1.1 client that does not support persistent connections MUST
include the "close" connection option in every request message.
An HTTP/1.1 server that does not support persistent connections MUST
include the "close" connection option in every response message that
does not have a 1xx (Informational) status code.
A system receiving an HTTP/1.0 (or lower-version) message that
includes a Connection header field MUST, for each connection-token in this
field, remove and ignore any header field(s) from the message with
the same name as the connection-token. This protects against mistaken
forwarding of such header fields by pre-HTTP/1.1 proxies. See .
The "Content-Length" header field indicates the size of the
message-body, in decimal number of octets, for any message other than
a response to the HEAD method or a response with a status code of 304.
In the case of responses to the HEAD method, it indicates the size of
the payload body (not including any potential transfer-coding) that
would have been sent had the request been a GET.
In the case of the 304 (Not Modified) response, it indicates the size of
the payload body (not including any potential transfer-coding) that
would have been sent in a 200 (OK) response.
An example is
Implementations SHOULD use this field to indicate the message-body
length when no transfer-coding is being applied and the
payload's body length can be determined prior to being transferred.
describes how recipients determine the length
of a message-body.
Any Content-Length greater than or equal to zero is a valid value.
Note that the use of this field in HTTP is significantly different from
the corresponding definition in MIME, where it is an optional field
used within the "message/external-body" content-type.
The "Date" general-header field represents the date and time at which
the message was originated, having the same semantics as the Origination
Date Field (orig-date) defined in Section 3.6.1 of .
The field value is an HTTP-date, as described in ;
it MUST be sent in rfc1123-date format.
An example is
Origin servers MUST include a Date header field in all responses,
except in these cases:
If the response status code is 100 (Continue) or 101 (Switching
Protocols), the response MAY include a Date header field, at
the server's option.If the response status code conveys a server error, e.g., 500
(Internal Server Error) or 503 (Service Unavailable), and it is
inconvenient or impossible to generate a valid Date.If the server does not have a clock that can provide a
reasonable approximation of the current time, its responses
MUST NOT include a Date header field. In this case, the rules
in MUST be followed.
A received message that does not have a Date header field MUST be
assigned one by the recipient if the message will be cached by that
recipient or gatewayed via a protocol which requires a Date.
Clients can use the Date header field as well; in order to keep request
messages small, they are advised not to include it when it doesn't convey
any useful information (as it is usually the case for requests that do not
contain a payload).
The HTTP-date sent in a Date header field SHOULD NOT represent a date and
time subsequent to the generation of the message. It SHOULD represent
the best available approximation of the date and time of message
generation, unless the implementation has no means of generating a
reasonably accurate date and time. In theory, the date ought to
represent the moment just before the payload is generated. In
practice, the date can be generated at any time during the message
origination without affecting its semantic value.
Some origin server implementations might not have a clock available.
An origin server without a clock MUST NOT assign Expires or Last-Modified
values to a response, unless these values were associated
with the resource by a system or user with a reliable clock. It MAY
assign an Expires value that is known, at or before server
configuration time, to be in the past (this allows "pre-expiration"
of responses without storing separate Expires values for each
resource).
The "Host" request-header field specifies the Internet host and port
number of the resource being requested, allowing the origin server or
gateway to differentiate between internally-ambiguous URLs, such as the root
"/" URL of a server for multiple host names on a single IP address.
The Host field value MUST represent the naming authority of the origin
server or gateway given by the original URL obtained from the user or
referring resource (generally an http URI, as described in
).
A "host" without any trailing port information implies the default
port for the service requested (e.g., "80" for an HTTP URL). For
example, a request on the origin server for
<http://www.example.org/pub/WWW/> would properly include:
A client MUST include a Host header field in all HTTP/1.1 request
messages. If the requested URI does not include an Internet host
name for the service being requested, then the Host header field MUST
be given with an empty value. An HTTP/1.1 proxy MUST ensure that any
request message it forwards does contain an appropriate Host header
field that identifies the service being requested by the proxy. All
Internet-based HTTP/1.1 servers MUST respond with a 400 (Bad Request)
status code to any HTTP/1.1 request message which lacks a Host header
field.
See Sections
and
for other requirements relating to Host.
The "TE" request-header field indicates what extension transfer-codings
it is willing to accept in the response, and whether or not it is
willing to accept trailer fields in a chunked transfer-coding.
Its value consists of the keyword "trailers" and/or a comma-separated
list of extension transfer-coding names with optional accept
parameters (as described in ).
The presence of the keyword "trailers" indicates that the client is
willing to accept trailer fields in a chunked transfer-coding, as
defined in . This keyword is reserved for use with
transfer-coding values even though it does not itself represent a
transfer-coding.
Examples of its use are:
The TE header field only applies to the immediate connection.
Therefore, the keyword MUST be supplied within a Connection header
field () whenever TE is present in an HTTP/1.1 message.
A server tests whether a transfer-coding is acceptable, according to
a TE field, using these rules:
The "chunked" transfer-coding is always acceptable. If the
keyword "trailers" is listed, the client indicates that it is
willing to accept trailer fields in the chunked response on
behalf of itself and any downstream clients. The implication is
that, if given, the client is stating that either all
downstream clients are willing to accept trailer fields in the
forwarded response, or that it will attempt to buffer the
response on behalf of downstream recipients.
Note: HTTP/1.1 does not define any means to limit the size of a
chunked response such that a client can be assured of buffering
the entire response.If the transfer-coding being tested is one of the transfer-codings
listed in the TE field, then it is acceptable unless it
is accompanied by a qvalue of 0. (As defined in , a
qvalue of 0 means "not acceptable".)If multiple transfer-codings are acceptable, then the
acceptable transfer-coding with the highest non-zero qvalue is
preferred. The "chunked" transfer-coding always has a qvalue
of 1.
If the TE field-value is empty or if no TE field is present, the only
transfer-coding is "chunked". A message with no transfer-coding is
always acceptable.
The "Trailer" general-header field indicates that the given set of
header fields is present in the trailer of a message encoded with
chunked transfer-coding.
An HTTP/1.1 message SHOULD include a Trailer header field in a
message using chunked transfer-coding with a non-empty trailer. Doing
so allows the recipient to know which header fields to expect in the
trailer.
If no Trailer header field is present, the trailer SHOULD NOT include
any header fields. See for restrictions on the use of
trailer fields in a "chunked" transfer-coding.
Message header fields listed in the Trailer header field MUST NOT
include the following header fields:
Transfer-EncodingContent-LengthTrailer
The "Transfer-Encoding" general-header field indicates what transfer-codings
(if any) have been applied to the message body. It differs from
Content-Encoding (Section 2.2 of ) in that transfer-codings are a property
of the message (and therefore are removed by intermediaries), whereas
content-codings are not.
Transfer-codings are defined in . An example is:
If multiple encodings have been applied to a representation, the transfer-codings
MUST be listed in the order in which they were applied.
Additional information about the encoding parameters MAY be provided
by other header fields not defined by this specification.
Many older HTTP/1.0 applications do not understand the Transfer-Encoding
header field.
The "Upgrade" general-header field allows the client to specify what
additional communication protocols it would like to use, if the server
chooses to switch protocols. Additionally, the server MUST use the Upgrade
header field within a 101 (Switching Protocols) response to indicate which
protocol(s) are being switched to.
For example,
The Upgrade header field is intended to provide a simple mechanism
for transition from HTTP/1.1 to some other, incompatible protocol. It
does so by allowing the client to advertise its desire to use another
protocol, such as a later version of HTTP with a higher major version
number, even though the current request has been made using HTTP/1.1.
This eases the difficult transition between incompatible protocols by
allowing the client to initiate a request in the more commonly
supported protocol while indicating to the server that it would like
to use a "better" protocol if available (where "better" is determined
by the server, possibly according to the nature of the method and/or
resource being requested).
The Upgrade header field only applies to switching application-layer
protocols upon the existing transport-layer connection. Upgrade
cannot be used to insist on a protocol change; its acceptance and use
by the server is optional. The capabilities and nature of the
application-layer communication after the protocol change is entirely
dependent upon the new protocol chosen, although the first action
after changing the protocol MUST be a response to the initial HTTP
request containing the Upgrade header field.
The Upgrade header field only applies to the immediate connection.
Therefore, the upgrade keyword MUST be supplied within a Connection
header field () whenever Upgrade is present in an
HTTP/1.1 message.
The Upgrade header field cannot be used to indicate a switch to a
protocol on a different connection. For that purpose, it is more
appropriate to use a 301, 302, 303, or 305 redirection response.
This specification only defines the protocol name "HTTP" for use by
the family of Hypertext Transfer Protocols, as defined by the HTTP
version rules of and future updates to this
specification. Additional tokens can be registered with IANA using the
registration procedure defined below.
The HTTP Upgrade Token Registry defines the name space for product
tokens used to identify protocols in the Upgrade header field.
Each registered token is associated with contact information and
an optional set of specifications that details how the connection
will be processed after it has been upgraded.
Registrations are allowed on a First Come First Served basis as
described in Section 4.1 of . The
specifications need not be IETF documents or be subject to IESG review.
Registrations are subject to the following rules:
A token, once registered, stays registered forever.The registration MUST name a responsible party for the
registration.The registration MUST name a point of contact.The registration MAY name a set of specifications associated with that
token. Such specifications need not be publicly available.The responsible party MAY change the registration at any time.
The IANA will keep a record of all such changes, and make them
available upon request.The responsible party for the first registration of a "product"
token MUST approve later registrations of a "version" token
together with that "product" token before they can be registered.If absolutely required, the IESG MAY reassign the responsibility
for a token. This will normally only be used in the case when a
responsible party cannot be contacted.
The "Via" general-header field MUST be used by gateways and proxies to
indicate the intermediate protocols and recipients between the user
agent and the server on requests, and between the origin server and
the client on responses. It is analogous to the "Received" field defined in
Section 3.6.7 of and is intended to be used for tracking message forwards,
avoiding request loops, and identifying the protocol capabilities of
all senders along the request/response chain.
The received-protocol indicates the protocol version of the message
received by the server or client along each segment of the
request/response chain. The received-protocol version is appended to
the Via field value when the message is forwarded so that information
about the protocol capabilities of upstream applications remains
visible to all recipients.
The protocol-name is optional if and only if it would be "HTTP". The
received-by field is normally the host and optional port number of a
recipient server or client that subsequently forwarded the message.
However, if the real host is considered to be sensitive information,
it MAY be replaced by a pseudonym. If the port is not given, it MAY
be assumed to be the default port of the received-protocol.
Multiple Via field values represent each proxy or gateway that has
forwarded the message. Each recipient MUST append its information
such that the end result is ordered according to the sequence of
forwarding applications.
Comments MAY be used in the Via header field to identify the software
of the recipient proxy or gateway, analogous to the User-Agent and
Server header fields. However, all comments in the Via field are
optional and MAY be removed by any recipient prior to forwarding the
message.
For example, a request message could be sent from an HTTP/1.0 user
agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
forward the request to a public proxy at p.example.net, which completes
the request by forwarding it to the origin server at www.example.com.
The request received by www.example.com would then have the following
Via header field:
Proxies and gateways used as a portal through a network firewall
SHOULD NOT, by default, forward the names and ports of hosts within
the firewall region. This information SHOULD only be propagated if
explicitly enabled. If not enabled, the received-by host of any host
behind the firewall SHOULD be replaced by an appropriate pseudonym
for that host.
For organizations that have strong privacy requirements for hiding
internal structures, a proxy MAY combine an ordered subsequence of
Via header field entries with identical received-protocol values into
a single such entry. For example,
could be collapsed to
Applications SHOULD NOT combine multiple entries unless they are all
under the same organizational control and the hosts have already been
replaced by pseudonyms. Applications MUST NOT combine entries which
have different received-protocol values.
The Message Header Field Registry located at shall be updated
with the permanent registrations below (see ):
Header Field NameProtocolStatusReferenceConnectionhttpstandardContent-LengthhttpstandardDatehttpstandardHosthttpstandardTEhttpstandardTrailerhttpstandardTransfer-EncodinghttpstandardUpgradehttpstandardViahttpstandard
The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
The entries for the "http" and "https" URI Schemes in the registry located at
shall be updated to point to Sections
and of this document
(see ).
This document serves as the specification for the Internet media types
"message/http" and "application/http". The following is to be registered with
IANA (see ).
The message/http type can be used to enclose a single HTTP request or
response message, provided that it obeys the MIME restrictions for all
"message" types regarding line length and encodings.
message
http
none
version, msgtype
The HTTP-Version number of the enclosed message
(e.g., "1.1"). If not present, the version can be
determined from the first line of the body.
The message type -- "request" or "response". If not
present, the type can be determined from the first
line of the body.
only "7bit", "8bit", or "binary" are permitted
none
none
This specification (see ).
nonenonenone
See Authors Section.
COMMON
none
IESG
The application/http type can be used to enclose a pipeline of one or more
HTTP request or response messages (not intermixed).
application
http
none
version, msgtype
The HTTP-Version number of the enclosed messages
(e.g., "1.1"). If not present, the version can be
determined from the first line of the body.
The message type -- "request" or "response". If not
present, the type can be determined from the first
line of the body.
HTTP messages enclosed by this type
are in "binary" format; use of an appropriate
Content-Transfer-Encoding is required when
transmitted via E-mail.
none
none
This specification (see ).
nonenonenone
See Authors Section.
COMMON
none
IESG
The registration procedure for HTTP Transfer Codings is now defined by
of this document.
The HTTP Transfer Codings Registry located at
shall be updated with the registrations below:
NameDescriptionReferencechunkedTransfer in a series of chunkscompressUNIX "compress" program methoddeflate"deflate" compression mechanism () used inside
the "zlib" data format ()
gzipSame as GNU zip
The registration procedure for HTTP Upgrade Tokens -- previously defined
in Section 7.2 of -- is now defined
by of this document.
The HTTP Status Code Registry located at
shall be updated with the registration below:
ValueDescriptionReferenceHTTPHypertext Transfer Protocol of this specification
This section is meant to inform application developers, information
providers, and users of the security limitations in HTTP/1.1 as
described by this document. The discussion does not include
definitive solutions to the problems revealed, though it does make
some suggestions for reducing security risks.
HTTP clients are often privy to large amounts of personal information
(e.g., the user's name, location, mail address, passwords, encryption
keys, etc.), and SHOULD be very careful to prevent unintentional
leakage of this information.
We very strongly recommend that a convenient interface be provided
for the user to control dissemination of such information, and that
designers and implementors be particularly careful in this area.
History shows that errors in this area often create serious security
and/or privacy problems and generate highly adverse publicity for the
implementor's company.
A server is in the position to save personal data about a user's
requests which might identify their reading patterns or subjects of
interest. This information is clearly confidential in nature and its
handling can be constrained by law in certain countries. People using
HTTP to provide data are responsible for ensuring that
such material is not distributed without the permission of any
individuals that are identifiable by the published results.
Implementations of HTTP origin servers SHOULD be careful to restrict
the documents returned by HTTP requests to be only those that were
intended by the server administrators. If an HTTP server translates
HTTP URIs directly into file system calls, the server MUST take
special care not to serve files that were not intended to be
delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
other operating systems use ".." as a path component to indicate a
directory level above the current one. On such a system, an HTTP
server MUST disallow any such construct in the request-target if it
would otherwise allow access to a resource outside those intended to
be accessible via the HTTP server. Similarly, files intended for
reference only internally to the server (such as access control
files, configuration files, and script code) MUST be protected from
inappropriate retrieval, since they might contain sensitive
information. Experience has shown that minor bugs in such HTTP server
implementations have turned into security risks.
Clients using HTTP rely heavily on the Domain Name Service, and are
thus generally prone to security attacks based on the deliberate
mis-association of IP addresses and DNS names. Clients need to be
cautious in assuming the continuing validity of an IP number/DNS name
association.
In particular, HTTP clients SHOULD rely on their name resolver for
confirmation of an IP number/DNS name association, rather than
caching the result of previous host name lookups. Many platforms
already can cache host name lookups locally when appropriate, and
they SHOULD be configured to do so. It is proper for these lookups to
be cached, however, only when the TTL (Time To Live) information
reported by the name server makes it likely that the cached
information will remain useful.
If HTTP clients cache the results of host name lookups in order to
achieve a performance improvement, they MUST observe the TTL
information reported by DNS.
If HTTP clients do not observe this rule, they could be spoofed when
a previously-accessed server's IP address changes. As network
renumbering is expected to become increasingly common , the
possibility of this form of attack will grow. Observing this
requirement thus reduces this potential security vulnerability.
This requirement also improves the load-balancing behavior of clients
for replicated servers using the same DNS name and reduces the
likelihood of a user's experiencing failure in accessing sites which
use that strategy.
By their very nature, HTTP proxies are men-in-the-middle, and
represent an opportunity for man-in-the-middle attacks. Compromise of
the systems on which the proxies run can result in serious security
and privacy problems. Proxies have access to security-related
information, personal information about individual users and
organizations, and proprietary information belonging to users and
content providers. A compromised proxy, or a proxy implemented or
configured without regard to security and privacy considerations,
might be used in the commission of a wide range of potential attacks.
Proxy operators need to protect the systems on which proxies run as
they would protect any system that contains or transports sensitive
information. In particular, log information gathered at proxies often
contains highly sensitive personal information, and/or information
about organizations. Log information needs to be carefully guarded, and
appropriate guidelines for use need to be developed and followed.
().
Proxy implementors need to consider the privacy and security
implications of their design and coding decisions, and of the
configuration options they provide to proxy operators (especially the
default configuration).
Users of a proxy need to be aware that proxies are no trustworthier than
the people who run them; HTTP itself cannot solve this problem.
The judicious use of cryptography, when appropriate, might suffice to
protect against a broad range of security and privacy attacks. Such
cryptography is beyond the scope of the HTTP/1.1 specification.
They exist. They are hard to defend against. Research continues.
Beware.
HTTP has evolved considerably over the years. It has
benefited from a large and active developer community--the many
people who have participated on the www-talk mailing list--and it is
that community which has been most responsible for the success of
HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
VanHeyningen deserve special recognition for their efforts in
defining early aspects of the protocol.
This document has benefited greatly from the comments of all those
participating in the HTTP-WG. In addition to those already mentioned,
the following individuals have contributed to this specification:
Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
Simon E. Spero, Richard N. Taylor, Robert S. Thau,
Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
Thanks to the "cave men" of Palo Alto. You know who you are.
Jim Gettys (the editor of ) wishes particularly
to thank Roy Fielding, the editor of , along
with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
Larry Masinter for their help. And thanks go particularly to Jeff
Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
Frystyk implemented RFC 2068 early, and we wish to thank them for the
discovery of many of the problems that this document attempts to
rectify.
This specification makes heavy use of the augmented BNF and generic
constructs defined by David H. Crocker for . Similarly, it
reuses many of the definitions provided by Nathaniel Borenstein and
Ned Freed for MIME . We hope that their inclusion in this
specification will help reduce past confusion over the relationship
between HTTP and Internet mail message formats.
Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
International Organization for StandardizationHTTP/1.1, part 2: Message SemanticsDay Softwarefielding@gbiv.comAlcatel-Lucent Bell Labsjg@freedesktop.orgHewlett-Packard CompanyJeffMogul@acm.orgMicrosoft Corporationhenrikn@microsoft.comAdobe Systems, IncorporatedLMM@acm.orgMicrosoft Corporationpaulle@microsoft.comWorld Wide Web Consortiumtimbl@w3.orgWorld Wide Web Consortiumylafon@w3.orggreenbytes GmbHjulian.reschke@greenbytes.deHTTP/1.1, part 3: Message Payload and Content NegotiationDay Softwarefielding@gbiv.comAlcatel-Lucent Bell Labsjg@freedesktop.orgHewlett-Packard CompanyJeffMogul@acm.orgMicrosoft Corporationhenrikn@microsoft.comAdobe Systems, IncorporatedLMM@acm.orgMicrosoft Corporationpaulle@microsoft.comWorld Wide Web Consortiumtimbl@w3.orgWorld Wide Web Consortiumylafon@w3.orggreenbytes GmbHjulian.reschke@greenbytes.deHTTP/1.1, part 6: CachingDay Softwarefielding@gbiv.comAlcatel-Lucent Bell Labsjg@freedesktop.orgHewlett-Packard CompanyJeffMogul@acm.orgMicrosoft Corporationhenrikn@microsoft.comAdobe Systems, IncorporatedLMM@acm.orgMicrosoft Corporationpaulle@microsoft.comWorld Wide Web Consortiumtimbl@w3.orgWorld Wide Web Consortiumylafon@w3.orgmnot@mnot.netgreenbytes GmbHjulian.reschke@greenbytes.deAugmented BNF for Syntax Specifications: ABNFBrandenburg InternetWorkingdcrocker@bbiw.netTHUS plc.paul.overell@thus.netKey words for use in RFCs to Indicate Requirement LevelsHarvard Universitysob@harvard.eduUniform Resource Identifier (URI): Generic SyntaxWorld Wide Web Consortiumtimbl@w3.orghttp://www.w3.org/People/Berners-Lee/Day Softwarefielding@gbiv.comhttp://roy.gbiv.com/Adobe Systems IncorporatedLMM@acm.orghttp://larry.masinter.net/Coded Character Set -- 7-bit American Standard Code for Information InterchangeAmerican National Standards InstituteZLIB Compressed Data Format Specification version 3.3Aladdin Enterprisesghost@aladdin.com
RFC 1950 is an Informational RFC, thus it might be less stable than
this specification. On the other hand, this downward reference was
present since the publication of RFC 2068 in 1997 (),
therefore it is unlikely to cause problems in practice. See also
.
DEFLATE Compressed Data Format Specification version 1.3Aladdin Enterprisesghost@aladdin.com
RFC 1951 is an Informational RFC, thus it might be less stable than
this specification. On the other hand, this downward reference was
present since the publication of RFC 2068 in 1997 (),
therefore it is unlikely to cause problems in practice. See also
.
GZIP file format specification version 4.3Aladdin Enterprisesghost@aladdin.comgzip@prep.ai.mit.edumadler@alumni.caltech.edughost@aladdin.comrandeg@alumni.rpi.edu
RFC 1952 is an Informational RFC, thus it might be less stable than
this specification. On the other hand, this downward reference was
present since the publication of RFC 2068 in 1997 (),
therefore it is unlikely to cause problems in practice. See also
.
Network Performance Effects of HTTP/1.1, CSS1, and PNGImproving HTTP LatencyRequirements for Internet Hosts - Application and SupportUniversity of Southern California (USC), Information Sciences InstituteBraden@ISI.EDURenumbering Needs WorkCERN, Computing and Networks Divisionbrian@dxcoms.cern.chcisco Systemsyakov@cisco.comHypertext Transfer Protocol -- HTTP/1.0MIT, Laboratory for Computer Sciencetimbl@w3.orgUniversity of California, Irvine, Department of Information and Computer Sciencefielding@ics.uci.eduW3 Consortium, MIT Laboratory for Computer Sciencefrystyk@w3.orgMultipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message BodiesInnosoft International, Inc.ned@innosoft.comFirst Virtual Holdingsnsb@nsb.fv.comMIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII TextUniversity of Tennesseemoore@cs.utk.eduHypertext Transfer Protocol -- HTTP/1.1University of California, Irvine, Department of Information and Computer Sciencefielding@ics.uci.eduMIT Laboratory for Computer Sciencejg@w3.orgDigital Equipment Corporation, Western Research Laboratorymogul@wrl.dec.comMIT Laboratory for Computer Sciencefrystyk@w3.orgMIT Laboratory for Computer Sciencetimbl@w3.orgHTTP State Management MechanismBell Laboratories, Lucent Technologiesdmk@bell-labs.comNetscape Communications Corp.montulli@netscape.comUse and Interpretation of HTTP Version NumbersWestern Research Laboratorymogul@wrl.dec.comDepartment of Information and Computer Sciencefielding@ics.uci.eduMIT Laboratory for Computer Sciencejg@w3.orgW3 Consortiumfrystyk@w3.orgHypertext Transfer Protocol -- HTTP/1.1University of California, Irvinefielding@ics.uci.eduW3Cjg@w3.orgCompaq Computer Corporationmogul@wrl.dec.comMIT Laboratory for Computer Sciencefrystyk@w3.orgXerox Corporationmasinter@parc.xerox.comMicrosoft Corporationpaulle@microsoft.comW3Ctimbl@w3.orgUpgrading to TLS Within HTTP/1.14K Associates / UC Irvinerohit@4K-associates.comAgranat Systems, Inc.lawrence@agranat.comHTTP Over TLSRTFM, Inc.ekr@rtfm.comHTTP State Management MechanismBell Laboratories, Lucent Technologiesdmk@bell-labs.comEpinions.com, Inc.lou@montulli.orgRegistration Procedures for Message Header FieldsNine by NineGK-IETF@ninebynine.orgBEA Systemsmnot@pobox.comHP LabsJeffMogul@acm.orgMedia Type Specifications and Registration ProceduresSun Microsystemsned.freed@mrochek.comklensin+ietf@jck.comGuidelines and Registration Procedures for New URI SchemesAT&T Laboratoriestony+urireg@maillennium.att.comQualcomm, Inc.hardie@qualcomm.comAdobe SystemsLMM@acm.orgGuidelines for Writing an IANA Considerations Section in RFCsIBMnarten@us.ibm.comGoogleHarald@Alvestrand.noInternet Message FormatQualcomm IncorporatedHandling Normative References to Standards-Track Documentsklensin+ietf@jck.comMIThartmans-ietf@mit.eduHTTP Cookies: Standards, Privacy, and PoliticsAnalysis of HTTP Performance ProblemsAnalysis of HTTP PerformanceUSC/Information Sciences Institutetouch@isi.eduUSC/Information Sciences Institutejohnh@isi.eduUSC/Information Sciences Institutekatia@isi.edu(original report dated Aug. 1996)
Although this document specifies the requirements for the generation
of HTTP/1.1 messages, not all applications will be correct in their
implementation. We therefore recommend that operational applications
be tolerant of deviations whenever those deviations can be
interpreted unambiguously.
Clients SHOULD be tolerant in parsing the Status-Line and servers
SHOULD be tolerant when parsing the Request-Line. In particular, they
SHOULD accept any amount of WSP characters between fields, even though
only a single SP is required.
The line terminator for header fields is the sequence CRLF.
However, we recommend that applications, when parsing such headers fields,
recognize a single LF as a line terminator and ignore the leading CR.
The character set of a representation SHOULD be labeled as the lowest
common denominator of the character codes used within that representation, with
the exception that not labeling the representation is preferred over labeling
the representation with the labels US-ASCII or ISO-8859-1. See .
Additional rules for requirements on parsing and encoding of dates
and other potential problems with date encodings include:
HTTP/1.1 clients and caches SHOULD assume that an RFC-850 date
which appears to be more than 50 years in the future is in fact
in the past (this helps solve the "year 2000" problem).Although all date formats are specified to be case-sensitive,
recipients SHOULD match day, week and timezone names
case-insensitively.An HTTP/1.1 implementation MAY internally represent a parsed
Expires date as earlier than the proper value, but MUST NOT
internally represent a parsed Expires date as later than the
proper value.All expiration-related calculations MUST be done in GMT. The
local time zone MUST NOT influence the calculation or comparison
of an age or expiration time.If an HTTP header field incorrectly carries a date value with a time
zone other than GMT, it MUST be converted into GMT using the
most conservative possible conversion.
HTTP has been in use by the World-Wide Web global information initiative
since 1990. The first version of HTTP, later referred to as HTTP/0.9,
was a simple protocol for hypertext data transfer across the Internet
with only a single method and no metadata.
HTTP/1.0, as defined by , added a range of request
methods and MIME-like messaging that could include metadata about the data
transferred and modifiers on the request/response semantics. However,
HTTP/1.0 did not sufficiently take into consideration the effects of
hierarchical proxies, caching, the need for persistent connections, or
name-based virtual hosts. The proliferation of incompletely-implemented
applications calling themselves "HTTP/1.0" further necessitated a
protocol version change in order for two communicating applications
to determine each other's true capabilities.
HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
requirements that enable reliable implementations, adding only
those new features that will either be safely ignored by an HTTP/1.0
recipient or only sent when communicating with a party advertising
compliance with HTTP/1.1.
It is beyond the scope of a protocol specification to mandate
compliance with previous versions. HTTP/1.1 was deliberately
designed, however, to make supporting previous versions easy. It is
worth noting that, at the time of composing this specification, we would
expect general-purpose HTTP/1.1 servers to:
understand any valid request in the format of HTTP/1.0 and
1.1;respond appropriately with a message in the same major version
used by the client.
And we would expect HTTP/1.1 clients to:
understand any valid response in the format of HTTP/1.0 or
1.1.
For most implementations of HTTP/1.0, each connection is established
by the client prior to the request and closed by the server after
sending the response. Some implementations implement the Keep-Alive
version of persistent connections described in Section 19.7.1 of .
This section summarizes major differences between versions HTTP/1.0
and HTTP/1.1.
The requirements that clients and servers support the Host request-header
field (), report an error if it is
missing from an HTTP/1.1 request, and accept absolute URIs ()
are among the most important changes defined by this
specification.
Older HTTP/1.0 clients assumed a one-to-one relationship of IP
addresses and servers; there was no other established mechanism for
distinguishing the intended server of a request than the IP address
to which that request was directed. The changes outlined above will
allow the Internet, once older HTTP clients are no longer common, to
support multiple Web sites from a single IP address, greatly
simplifying large operational Web servers, where allocation of many
IP addresses to a single host has created serious problems. The
Internet will also be able to recover the IP addresses that have been
allocated for the sole purpose of allowing special-purpose domain
names to be used in root-level HTTP URLs. Given the rate of growth of
the Web, and the number of servers already deployed, it is extremely
important that all implementations of HTTP (including updates to
existing HTTP/1.0 applications) correctly implement these
requirements:
Both clients and servers MUST support the Host request-header field.A client that sends an HTTP/1.1 request MUST send a Host header field.Servers MUST report a 400 (Bad Request) error if an HTTP/1.1
request does not include a Host request-header field.Servers MUST accept absolute URIs.
Some clients and servers might wish to be compatible with some
previous implementations of persistent connections in HTTP/1.0
clients and servers. Persistent connections in HTTP/1.0 are
explicitly negotiated as they are not the default behavior. HTTP/1.0
experimental implementations of persistent connections are faulty,
and the new facilities in HTTP/1.1 are designed to rectify these
problems. The problem was that some existing HTTP/1.0 clients might
send Keep-Alive to a proxy server that doesn't understand
Connection, which would then erroneously forward it to the next
inbound server, which would establish the Keep-Alive connection and
result in a hung HTTP/1.0 proxy waiting for the close on the
response. The result is that HTTP/1.0 clients must be prevented from
using Keep-Alive when talking to proxies.
However, talking to proxies is the most important use of persistent
connections, so that prohibition is clearly unacceptable. Therefore,
we need some other mechanism for indicating a persistent connection
is desired, which is safe to use even when talking to an old proxy
that ignores Connection. Persistent connections are the default for
HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
declaring non-persistence. See .
The original HTTP/1.0 form of persistent connections (the Connection:
Keep-Alive and Keep-Alive header field) is documented in Section 19.7.1 of .
Empty list elements in list productions have been deprecated.
()
Rules about implicit linear whitespace between certain grammar productions
have been removed; now it's only allowed when specifically pointed out
in the ABNF. The NUL character is no longer allowed in comment and quoted-string
text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
Non-ASCII content in header fields and reason phrase has been obsoleted and
made opaque (the TEXT rule was removed)
()
Clarify that HTTP-Version is case sensitive.
()
Require that invalid whitespace around field-names be rejected.
()
Require recipients to handle bogus Content-Length header fields as errors.
()
Remove reference to non-existent identity transfer-coding value tokens.
(Sections and
)
Update use of abs_path production from RFC 1808 to the path-absolute + query
components of RFC 3986.
()
Clarification that the chunk length does not include the count of the octets
in the chunk header and trailer. Furthermore disallowed line folding
in chunk extensions.
()
Remove hard limit of two connections per server.
()
Clarify exactly when close connection options must be sent.
()
Chunked-Body = *chunk last-chunk trailer-part CRLF
Connection = "Connection:" OWS Connection-v
Connection-v = *( "," OWS ) connection-token *( OWS "," [ OWS
connection-token ] )
Content-Length = "Content-Length:" OWS 1*Content-Length-v
Content-Length-v = 1*DIGIT
Date = "Date:" OWS Date-v
Date-v = HTTP-date
GMT = %x47.4D.54 ; GMT
HTTP-Prot-Name = %x48.54.54.50 ; HTTP
HTTP-Version = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
HTTP-date = rfc1123-date / obs-date
HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body
]
Host = "Host:" OWS Host-v
Host-v = uri-host [ ":" port ]
MIME-Version =
Method = token
OWS = *( [ obs-fold ] WSP )
Pragma =
RWS = 1*( [ obs-fold ] WSP )
Reason-Phrase = *( WSP / VCHAR / obs-text )
Request = Request-Line *( header-field CRLF ) CRLF [ message-body ]
Request-Line = Method SP request-target SP HTTP-Version CRLF
Response = Status-Line *( header-field CRLF ) CRLF [ message-body ]
Status-Code = 3DIGIT
Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
TE = "TE:" OWS TE-v
TE-v = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
Trailer = "Trailer:" OWS Trailer-v
Trailer-v = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
Transfer-Encoding = "Transfer-Encoding:" OWS Transfer-Encoding-v
Transfer-Encoding-v = *( "," OWS ) transfer-coding *( OWS "," [ OWS
transfer-coding ] )
URI-reference =
Upgrade = "Upgrade:" OWS Upgrade-v
Upgrade-v = *( "," OWS ) product *( OWS "," [ OWS product ] )
Via = "Via:" OWS Via-v
Via-v = *( "," OWS ) received-protocol RWS received-by [ RWS comment
] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
] )
Warning =
absolute-URI =
asctime-date = day-name SP date3 SP time-of-day SP year
attribute = token
authority =
chunk = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
chunk-data = 1*OCTET
chunk-ext = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
chunk-ext-name = token
chunk-ext-val = token / quoted-str-nf
chunk-size = 1*HEXDIG
comment = "(" *( ctext / quoted-cpair / comment ) ")"
connection-token = token
ctext = OWS / %x21-27 ; '!'-'''
/ %x2A-5B ; '*'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
date1 = day SP month SP year
date2 = day "-" month "-" 2DIGIT
date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
day = 2DIGIT
day-name = %x4D.6F.6E ; Mon
/ %x54.75.65 ; Tue
/ %x57.65.64 ; Wed
/ %x54.68.75 ; Thu
/ %x46.72.69 ; Fri
/ %x53.61.74 ; Sat
/ %x53.75.6E ; Sun
day-name-l = %x4D.6F.6E.64.61.79 ; Monday
/ %x54.75.65.73.64.61.79 ; Tuesday
/ %x57.65.64.6E.65.73.64.61.79 ; Wednesday
/ %x54.68.75.72.73.64.61.79 ; Thursday
/ %x46.72.69.64.61.79 ; Friday
/ %x53.61.74.75.72.64.61.79 ; Saturday
/ %x53.75.6E.64.61.79 ; Sunday
field-content = *( WSP / VCHAR / obs-text )
field-name = token
field-value = *( field-content / OWS )
general-header = Cache-Control / Connection / Date / Pragma / Trailer
/ Transfer-Encoding / Upgrade / Via / Warning / MIME-Version
header-field = field-name ":" OWS [ field-value ] OWS
hour = 2DIGIT
http-URI = "http://" authority path-abempty [ "?" query ]
https-URI = "https://" authority path-abempty [ "?" query ]
last-chunk = 1*"0" *WSP [ chunk-ext ] CRLF
message-body = *OCTET
minute = 2DIGIT
month = %x4A.61.6E ; Jan
/ %x46.65.62 ; Feb
/ %x4D.61.72 ; Mar
/ %x41.70.72 ; Apr
/ %x4D.61.79 ; May
/ %x4A.75.6E ; Jun
/ %x4A.75.6C ; Jul
/ %x41.75.67 ; Aug
/ %x53.65.70 ; Sep
/ %x4F.63.74 ; Oct
/ %x4E.6F.76 ; Nov
/ %x44.65.63 ; Dec
obs-date = rfc850-date / asctime-date
obs-fold = CRLF
obs-text = %x80-FF
partial-URI = relative-part [ "?" query ]
path-abempty =
path-absolute =
port =
product = token [ "/" product-version ]
product-version = token
protocol-name = token
protocol-version = token
pseudonym = token
qdtext = OWS / "!" / %x23-5B ; '#'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
qdtext-nf = WSP / "!" / %x23-5B ; '#'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
query =
quoted-cpair = "\" ( WSP / VCHAR / obs-text )
quoted-pair = "\" ( WSP / VCHAR / obs-text )
quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
received-by = ( uri-host [ ":" port ] ) / pseudonym
received-protocol = [ protocol-name "/" ] protocol-version
relative-part =
request-header =
request-target = "*" / absolute-URI / ( path-absolute [ "?" query ] )
/ authority
response-header =
rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
second = 2DIGIT
special = "(" / ")" / "" / "@" / "," / ";" / ":" / "\" /
DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
start-line = Request-Line / Status-Line
t-codings = "trailers" / ( transfer-extension [ te-params ] )
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
"^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
te-ext = OWS ";" OWS token [ "=" word ]
te-params = OWS ";" OWS "q=" qvalue *te-ext
time-of-day = hour ":" minute ":" second
token = 1*tchar
trailer-part = *( header-field CRLF )
transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /
transfer-extension
transfer-extension = token *( OWS ";" OWS transfer-parameter )
transfer-parameter = attribute BWS "=" BWS value
uri-host =
value = word
word = token / quoted-string
year = 4DIGIT
]]>ABNF diagnostics:
Extracted relevant partitions from .
Closed issues:
:
"HTTP Version should be case sensitive"
()
:
"'unsafe' characters"
()
:
"Chunk Size Definition"
()
:
"Message Length"
()
:
"Media Type Registrations"
()
:
"URI includes query"
()
:
"No close on 1xx responses"
()
:
"Remove 'identity' token references"
()
:
"Import query BNF"
:
"qdtext BNF"
:
"Normative and Informative references"
:
"RFC2606 Compliance"
:
"RFC977 reference"
:
"RFC1700 references"
:
"inconsistency in date format explanation"
:
"Date reference typo"
:
"Informative references"
:
"ISO-8859-1 Reference"
:
"Normative up-to-date references"
Other changes:
Update media type registrations to use RFC4288 template.
Use names of RFC4234 core rules DQUOTE and WSP,
fix broken ABNF for chunk-data
(work in progress on )
Closed issues:
:
"Bodies on GET (and other) requests"
:
"Updating to RFC4288"
:
"Status Code and Reason Phrase"
:
"rel_path not used"
Ongoing work on ABNF conversion ():
Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
"trailer-part").
Avoid underscore character in rule names ("http_URL" ->
"http-URL", "abs_path" -> "path-absolute").
Add rules for terms imported from URI spec ("absoluteURI", "authority",
"path-absolute", "port", "query", "relativeURI", "host) -- these will
have to be updated when switching over to RFC3986.
Synchronize core rules with RFC5234.
Get rid of prose rules that span multiple lines.
Get rid of unused rules LOALPHA and UPALPHA.
Move "Product Tokens" section (back) into Part 1, as "token" is used
in the definition of the Upgrade header field.
Add explicit references to BNF syntax and rules imported from other parts of the specification.
Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
Closed issues:
:
"HTTP-date vs. rfc1123-date"
:
"WS in quoted-pair"
Ongoing work on IANA Message Header Field Registration ():
Reference RFC 3984, and update header field registrations for headers defined
in this document.
Ongoing work on ABNF conversion ():
Replace string literals when the string really is case-sensitive (HTTP-Version).
Closed issues:
:
"Connection closing"
:
"Move registrations and registry information to IANA Considerations"
:
"need new URL for PAD1995 reference"
:
"IANA Considerations: update HTTP URI scheme registration"
:
"Cite HTTPS URI scheme definition"
:
"List-type headers vs Set-Cookie"
Ongoing work on ABNF conversion ():
Replace string literals when the string really is case-sensitive (HTTP-Date).
Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
Closed issues:
:
"Out-of-date reference for URIs"
:
"RFC 2822 is updated by RFC 5322"
Ongoing work on ABNF conversion ():
Use "/" instead of "|" for alternatives.
Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
Only reference RFC 5234's core rules.
Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
whitespace ("OWS") and required whitespace ("RWS").
Rewrite ABNFs to spell out whitespace rules, factor out
header field value format definitions.
Closed issues:
:
"Header LWS"
:
"Sort 1.3 Terminology"
:
"RFC2047 encoded words"
:
"Character Encodings in TEXT"
:
"Line Folding"
:
"OPTIONS * and proxies"
:
"Reason-Phrase BNF"
:
"Use of TEXT"
:
"Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
:
"RFC822 reference left in discussion of date formats"
Final work on ABNF conversion ():
Rewrite definition of list rules, deprecate empty list elements.
Add appendix containing collected and expanded ABNF.
Other changes:
Rewrite introduction; add mostly new Architecture Section.
Move definition of quality values from Part 3 into Part 1;
make TE request header field grammar independent of accept-params (defined in Part 3).
Closed issues:
:
"base for numeric protocol elements"
:
"comment ABNF"
Partly resolved issues:
:
"205 Bodies" (took out language that implied that there might be
methods for which a request body MUST NOT be included)
:
"editorial improvements around HTTP-date"
Closed issues:
:
"Repeating single-value headers"
:
"increase connection limit"
:
"IP addresses in URLs"
:
"take over HTTP Upgrade Token Registry"
:
"CR and LF in chunk extension values"
:
"HTTP/0.9 support"
:
"pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
:
"move definitions of gzip/deflate/compress to part 1"
:
"disallow control characters in quoted-pair"
Partly resolved issues:
:
"update IANA requirements wrt Transfer-Coding values" (add the
IANA Considerations subsection)
Closed issues:
:
"header parsing, treatment of leading and trailing OWS"
Partly resolved issues:
:
"Placement of 13.5.1 and 13.5.2"
:
"use of term "word" when talking about header structure"
Closed issues:
:
"Clarification of the term 'deflate'"
:
"OPTIONS * and proxies"
:
"MIME-Version not listed in P1, general header fields"
:
"IANA registry for content/transfer encodings"
:
"Case-sensitivity of HTTP-date"
:
"use of term "word" when talking about header structure"
Partly resolved issues:
:
"Term for the requested resource's URI"
Closed issues:
:
"Connection Closing"
:
"Delimiting messages with multipart/byteranges"
:
"Handling multiple Content-Length headers"
:
"Clarify entity / representation / variant terminology"
:
"consider removing the 'changes from 2068' sections"
Partly resolved issues:
:
"HTTP(s) URI scheme definitions"
Closed issues:
:
"Trailer requirements"
:
"Text about clock requirement for caches belongs in p6"
:
"effective request URI: handling of missing host in HTTP/1.0"
:
"confusing Date requirements for clients"
Partly resolved issues:
:
"Handling multiple Content-Length headers"